detach v.

the usual form of Latin dis- in Old Italian, Spanish, Portuguese, Provençal, and French. In Middle English, interchanging with dis- (which in a later period displaced it), hence such form as desarmen, desdein, deshonour, desparagen, deschargen, despisen, etc.

mid-14c. (mid-13c. in Anglo-Latin), "to take or seize (property or goods) by law," a legal term, from Old French atachier "fasten; arrest" (11c.), earlier estachier "to attach, fix; stake up, support" (Modern French attacher, also compare Italian attaccare), from a- "to" (see ad-) + a base also found in detach, perhaps from Frankish *stakon "a post, stake" or a similar Germanic word, from Proto-Germanic *stakon- "a stake," from PIE root *steg- (1) "pole, stick" (see stake (n.)).

The meaning "fasten, affix, connect," which probably is the original sense etymologically, is attested in English from c. 1400. Related: Attached; attaching.