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.
"affectionate, devoted, fond," 1793, past-participle adjective from attach in the sense of "join to or with in companionship or affection" (1765). Earlier the adjective meant "arrested" (1610s). The literal sense of "fastened on" is from 1841.
1835, from French attaché "junior officer attached to the staff of an ambassador, etc.," literally "attached," noun use of past participle of attacher "to attach" (see attach). Attache case "small leather case for carrying papers" is recorded by 1900.
c. 1400, attachement, "arrest of a person on judicial warrant" (mid-13c. in Anglo-Latin), from Anglo-French attachement, from Old French attacher "to attach" (see attach). The word's application to property (including, later, wages) is by 1590s; the meaning "sympathy, devotion" is recorded from 1704; that of "something that is attached to something else" dates from 1797 and has become very common since the rise of electronic mail.
also re-attach, "attach anew or again," in any sense, c. 1600 originally in legalese and now obsolete in that sense; see re- "back, again" + attach (v.). The general sense of "to attach again" is by 1813 and might be a new formation. Related: Reattached; reattaching; reattachment (1570s in the legal sense).
c. 1600, "assault, assail, begin hostilities against," from French attaquer (16c.), from Florentine Italian attaccare (battaglia) "join (battle)," thus the word is a doublet of attach, which was used 15c.-17c. also in the sense now reserved to attack.
The meaning "endeavor to bring into discredit by writing, proposals, etc." is from 1640s. The general sense of "begin action" is from 1670s, originally of diseases. Related: Attacked; attacking.