| Entry | Förklaring |
| M | Sømil, Mud, Ungarn (gl. nationsbogstav) |
| m | minut, meter, misvisende |
| M. | Mudder |
| m. | mørk |
| m/d | Months after date, Malicius damage |
| m/f | MotorFærge |
| m/m | Minimum/Maximum |
| m/r | Mates receipt |
| m/s | Motor ship |
| m/t | Motor tanker |
| m2 | kvadratmeter |
| m3 | kubikmeter |
| MA | Marocco (gl. nationsbogstav) |
| mA | milliampere |
| MACOR | Tidligere McGregor, salg/service af vandtætte lukkemidler, herunder luger, bovporte osv. |
| MAGDA | København Havn`s nye (mar. 1997) containerkran |
| MAMA | Maintenance Management, vedligeholdelsesprogram for maskiner fremstillet af Wärtsilä NSD. se også under MP2. |
| MAMS | Mobil Amos Maintenance System, system til olieanalyser. |
| MAMS-system | Mobil AMOS Maintenance System, computerbaseret informations- og vedligeholdelsessystem, udviklet af Mobil Oil og firmaet SpecTec. |
| MarAd | Maritime Administration. US kontor for statistik og analyse. |
| MARINA | De Filipinske Søfartsmyndigheder. |
| Maris | Maritime Informations Society |
| MARIS | Maritime Information Systems, VTS overvågning udført af RACAL Norway og Litton Marine i Norge, især rundt olieplatforme i Nordsøen. |
| MARPOL | International Convention for the Prevention og Pollution fron Ships. |
| Marsim | Maritime Simulator |
| MAS | Marinestation |
| Mask | Maskine |
| Mat Strut Ses | Advanced Materials and Design Procedures for Large Size Surface Effect Ships. (Europæisk forskningsprojekt vedr. hurtige transportmuligheder til søs). |
| mb | Mellem bølge, Medium wave |
| MB | Merchant broker |
| mb | Milibar, se hPa |
| mbr. | middelbredde |
| mbt | Motorblocks Turning |
| MCC | Master Control Center |
| MCD | Maritimt Center Danmark, maritim museumsforening, Svendborg. |
| MCI | Mærsk Container Industri |
| MCL | Melbridge Container Line |
| mco | Maximum Continuos Output |
| MCS | Meteo Consult Scandinavia, privat firma der sælger meteorologiske oplysninger til den maritime verden, etableret 1998. |
| MCS | Monitoring and Control System |
| MCTS | Maritime Computer and Technical Services |
| MCWW | Maritime Conveyance World Wide |
| md. | middag |
| MDAP | Mutual Defence Assistance Programme (våbenhjælp). |
| mdo | Marine Diesel Oil |
| mdse | Merchandise |
| mdwt | Metric Tons Dead Weight |
| ME | Maritime Engineering, Oslo |
| mech | Mechanical |
| Memac | Elektronisk maskinovervågning |
| MEPC | Marine Environment Protecion Committee, under IMO |
| MERSAR | Merchant Ship Search and Rescue Manual |
| MES-system | "Means of Rescue, især om ""tørskoet"" evakuering." |
| messrs | Messiurs, Gentlemen, Sirs |
| MF | Medium Frequency, Mellem Bølge |
| MF | Medium frequence (mellembølge) |
| MFAG | Medical First Aid Guide |
| MFAG | Medical First Aid Guide |
| mfg | Manufacturing |
| MFMS | Marine Fluid Management System, overvågning af flydende laster |
| mfrs | Manufactures |
| mg | milligram (tusindedel gram) |
| mg/r | Managing/manager |
| MGO | Marine GasOil |
| mgt | Management |
| MGT | Manila Grain Terminal |
| mh | Main Hatch |
| mhe | Materials Handling Equipment |
| MHHW | Mean Higher High Water (middelværdien af højeste højvande) |
| MHV | MarineHjemmeVærnet |
| MHW | Mean High Water (middelværdien af højvandshøjderne) |
| MHWN | Mean High Water Neaps (middelværdien af niptidshøjvandshøjderne) |
| mhws | Mean High Water Spring Tides |
| MHWS | Mean High Water Spring (middelværdien af springtidshøjvandshøjderne) |
| MHz | Mega Hertz |
| mic | Man in Charge |
| MICT | Manila International Container Terminal, se også ATI-terminal |
| MIF | Maritime Industries Forum |
| mil | Sømandssprogets mil er en sømil = 1852 meter = eet storcirkelminut. Skibets fart måles i knob, hvilket er det samme som sømil. |
| min | Minute, Minimum |
| min | minut |
| MISC | Malaysian International Shipping Company, containerrederi |
| misv. | misvisende |
| MIT | Manzanillo International Terminal, containerterminal i Panama |
| miti | Ministry, International Trade and Industry (japan). |
| MITS | Maritime Informations Teknologi |
| Mk | Malet mærke |
| mkl. | middelklokkeslettet |
| mkt | Market |
| ml | milliliter (tusindedel liter) |
| ML | Mean Level |
| mld | Moulded |
| MLLW | Mean Lower Low Water (middelværdien af laveste lavvandshøjderne) |
| MLOG | Forkortelse for søværnets mobile baseenhed på 30-40 lastbiler |
| MLW | Mean Low Water (middelværdien af niptidslavvandshøjderne) |
| MLWN | Mean Low Water Neaps (middelværdien af niptidslavvandshøjderne) |
| mlws | Mean Low Water Spring Tides |
| MLWS | Mean Low Water Springs (middelværdien af springtidslavvandshøjderne) |
| mm | millimeter |
| MMF | MaskinMesternes Forening |
| MMM | Mærsk Mc-Kinney Møller |
| MMPC | Motorship Marine Propulsion Conference |
| MMS | Marine Management Systems, samarbejde med ABS via Windows program til FleetWorks. |
| MMS | Mathisen Maritime Service, Long Beach USA, ejer: Palle B. Mathisen |
| MMSI | Maritime Mobile Service Identity, forskellige Coast Guards muligheder for at identificere skibe via VHF samt skibes GMDSS-nummer. Automatisk polling sker via bl.a. GMDSS Internationale nød/kaldekanal 70, samt alm. VHF. |
| mn. | midnat |
| MO | Monarco (gl. nationsbogstav) |
| Mo | Morse code light, blink i morsekode |
| moa | Memorandum of Agreement |
| MOB | Man Over Board(båd) |
| mod | Ministry of Defence |
| MOG | Mærsk Olie & Gas |
| moh | Medical Officer and Health |
| mol | More or Less |
| MOL | Mitsui Osk Line, Japansk linierederi |
| molchopt | More or less charters option |
| molco | More or less charteres option |
| moloo | More or less owners option |
| mom | Moment |
| Mon | monument |
| mop | Muriate of potash |
| mos | Months |
| MOT | Ministry of Transport (now Department of Transport), or monthly overtime |
| MOU | Memorandum of Understanding, se også PSC. |
| MOVA | Mobil vedligeholdelses afdeling, bruges af søværnet i Danmark |
| MP2 | Vedligeholdelsesprogram for Wärtsiläs maskiner, videreudvikling af MAMA, se dette. |
| mph | Miles per hour |
| mph. | miles per hour |
| mpp | Multipurpose |
| MR | Medium Range, bruges om tankskibstyper, se også LR |
| MRCC | Maritime Rescue Coordination Center |
| MRCC | Maritime Rescue Coordination Center (redningscenter) |
| MRD | Minerydningsdrone, fjernstyrede småfartøjer til søminerydning. |
| MRV | Marstal Reparations Værft |
| ms | Months after sight, Machinery survey |
| Ms | mussels (muslinger) |
| mS | medium sand |
| MSA | Marine Safety Agency, engelsk firma |
| MSA | Maritime Safety Authority |
| MSA | Merchant Shipping Act |
| MSC | Mediteranean Shipping Company |
| MSC | Military Sealift Command |
| MSC | Marine Safety Commitee, under IMO, møde nr. 64, dec. 1994 |
| MSF | Mindre Standard Fartøj, typebetegnelse i dansk søværn |
| MSG | Mittelstandische Serienschiffbau Desellchaft, samarbejde mellem ni mindre værfter i Tyskland. |
| MSL | Mean Sea Level |
| MSLV. | middelspringtidslavvande |
| MSO | Masters Standing orders |
| MSR | Maritime Systems Research. Vurdering af Maritime markedsforhold, ejet af A.P.Møller. |
| MSS | Maersk Supply Service |
| mst | Measurement. |
| MST | Mean Tide Level |
| MSTC | Marine Sience and Technology, Japansk marineingeniørfirma. |
| mt | Motortanker, empty, metric ton, mean time |
| MT | Malta (gl. nationsbogstav) |
| MTB | Motor Torpedo Båd |
| MTC | Maersk Training Center, Svendborg |
| MTC | Maritime Transport Committee |
| mths | Months |
| mtl | Mean Tidal Level |
| MUI | Maritime Union of Indian Officers |
| MUTOGI | Medarbejder Udvikling Til Olie- og GasIndustrien |
| mv | Motorvessel |
| mv. | misvisende |
| MW | Medium Wave |
| MX | Mexico (gl. nationsbogstav) |
| MY | Malaysia (gl. nationsbogstav) |
| mym | Mymeter, en tusindedel milimeter |
| mzd | meridianzenitdistance |