custom

\ \ [12] Custom comes ultimately from Latin consuēscere, a compound verb formed from the intensive prefix com- and suēscere ‘become accustomed’. This in turn was derived from suī, the genitive singular of the reflexive pronoun suus ‘oneself’; the notion underlying its formation was therefore ‘that which is one’s own’, a semantic element echoed in Greek ethos ‘custom, usage, trait’, which was based ultimately on Indo-European *swe- ‘oneself’.

\ \ From consuēscere was formed the Latin noun consuētūdō ‘being accustomed’ (source of the English legal noun consuetude ‘custom’ [14]).

\ \ This passed into early Old French as *costudne, which developed via *costumne to custome, the form borrowed into Middle English (English costume came from the same ultimate source, but via Italian costume). The word’s original sense, ‘habitual practice’, developed various secondary associations, including ‘customary tax’ (whence customs duties) and ‘customary business patronage’ (whence customer). The derivative accustom [15] was borrowed from Anglo-Norman acustumer.

\ \ Cf.⇒ ACCUSTOM, COSTUME