porthole (n.)

c. 1300 (mid 13c. in surnames), porte, "a gate, an entrance to a place, a portal; the gate of a town or fortress," also in names of specific gates, from Old French porte "gate, entrance," from Latin porta "a city gate, a gate; door, entrance," akin to portus "harbor," from PIE root *per- (2) "to lead, pass over." Old English also had occasional port in this sense, from Latin, but the Middle English word seems to be a new borrowing via French.

The meaning "porthole, an opening in the side of a ship" is attested from mid-14c.; in old warships, an embrasure in the side of the ship through which cannons are pointed. The medical sense of "place where something enters the body" is by 1908 probably short for portal. In computers, "place where signals enter or leave a data-transmission system," by 1979, from earlier use in electronics (1953) for "pair of terminals where a signal enters or leaves a network or device," which also probably is short for portal.

Old English hol (adj.) "hollow, concave;" as a noun, "hollow place; cave; orifice; perforation," from Proto-Germanic *hulan (source also of Old Saxon, Old Frisian, Old High German hol, Middle Dutch hool, Old Norse holr, German hohl "hollow," Gothic us-hulon "to hollow out"), from PIE root *kel- (1) "to cover, conceal, save." As an adjective, it has been displaced by hollow, which in Old English was only a noun, meaning "excavated habitation of certain wild animals."

As a contemptuous word for "small dingy lodging or abode" it is attested from 1610s. Meaning "a fix, scrape, mess" is from 1760. Obscene slang use for "vulva" is implied from mid-14c. Golfing hole-in-one is from 1914; as a verbal phrase from 1913. To need (something) like a hole in the head, applied to something useless or detrimental, first recorded 1944 in entertainment publications, probably a translation of a Yiddish expression such as ich darf es vi a loch in kop.