Английский Этимологический словарь - custom

- 12c., from O.Fr. costume, from V.L. *consuetumen, from L. consuetudinem, acc. of consuetudo "habit or usage," from consuetus, pp. of consuescere "accustom," from com- intens. prefix + suescere "become used to, accustom oneself," related to sui, gen. of suus "oneself," from PIE *swe- "oneself." Replaced O.E. юeaw. Sense of a "regular" toll or tax on goods is 14c. Customer (14c.) meant "customs official" before meaning switched to "buyer" (first attested 1409). Customary is from 1523.