"partially or loosely united," by 1860, from semi- + past participle of detach (v.). Compare semi-detached.
Entries linking to semi-attached
semi-
word-forming element of Latin origin meaning "half," also loosely, "part, partly; partial, almost; imperfect; twice," from Latin semi- "half" (before vowels often sem-, sometimes further reduced to se- before m-), from PIE *semi- "half" (source also of Sanskrit sami "half," Greek hēmi- "half," Old English sam-, Gothic sami- "half").
The Old English cognate, sam-, was used in such compounds as samhal "in poor health, weakly," literally "half-whole;" samsoden "half-cooked" ('half-sodden'), figuratively "stupid" (compare half-baked); samcucu "half-dead," etymologically "half-alive" (see quick (adj.)); and the lingering survivor, sandblind "dim-sighted" (q.v.).
The Latin element was common in formations from Late Latin, as in semi-gravis "half-drunk," semi-hora "half hour," semi-mortuus "half-dead," semi-nudus "half-naked," semi-vir "half-man, hermaphrodite."
The Latin-derived form in English has been active in forming native words since 15c. Semi-bousi "half-drunk" ('semi-boozy'), now obsolete, was among the earliest (c. 1400). As a noun, semi has variously been short for semi-detached house (by 1912), semi-trailer (by 1942), semi-final (by 1942).
detach v.
1680s, "unfasten, disunite" (transitive), especially "separate for a special purpose or service," from French détacher "to detach, untie," from Old French destachier, from des- "apart" (see des-) + attachier "attach" (see attach). Related: Detached; detaching.
semi-detached adj.
"partly united, partly attached," originally in reference to houses joined together by a party-wall but detached from other buildings, 1845, from semi- + past participle of detach (v.).
The "Detached House" bears its peculiar characteristic on its front; it stands alone, and nothing more can be said about it; but with the "semi-detached house" there is a subtle mystery, much to be marvelled at. Semi-detached! Have the party-walls between two houses shrunk, or is there a bridge connecting the two, as in Mr. Beckford's house in Landsdown Crescent, Bath? A semi-detached house may be a house with a field on one side and a bone-boiling factory on the other. Semi-detached may mean half-tumbling to pieces. I must inquire into it. ["Houses to Let," in Household Words, March 20, 1852]