naval officer, c. 1600, originally so called because he was stationed amidships when on duty (see amid). Midships as short for amidships is by 1620s. Midship as "the middle of a ship or boat" is from 1550s.
Entries linking to midshipman
amid adv., prep.
Middle English amidde, from Old English on middan "in the middle," from dative singular of midde "mid, middle" (from PIE root *medhyo- "middle"); also see a- (1). The phrase evidently was felt as "in (the) middle" and thus followed by a genitive case, and if this had endured we would follow it today with of. (See amidst for further evolution along this line).
The same applies to equivalents in Latin (in medio) and Greek (en meso), both originally adjective phrases which evolved to take the genitive case. But in later Old English on middan also was treated as a preposition and followed by dative. Used in compounds from early 13c.
mid adj.
"middle; being the middle part or midst; being between, intermediate," Old English mid, midd from Proto-Germanic *medja- (source also of Old Norse miðr, Old Saxon middi, Old Frisian midde, Middle Dutch mydde, Old High German mitti, German mitte, Gothic midjis "mid, middle"), from PIE root *medhyo- "middle."
By late Middle English probably felt as a prefix only, and now surviving in English only as a prefix (mid-air, midstream, etc.). Prefixed to months, seasons, etc. from late Old English. As a preposition, "in the middle of, amid" (c. 1400) it is from in midde or a shortened form of amid (compare midshipman) and sometimes is written 'mid.
middy n.
colloquial abbreviation of midshipman, by 1818. As "loose, long type of women's blouse," 1911, from resemblance to shirts worn by midshipmen.