c.1200, "habitual practice," 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" (see
idiom). Replaced O.E.
þeaw. Sense of a "regular" toll or tax on goods is c.1325.
Customer (14c.) meant "customs official" before meaning switched to "buyer" (first attested 1409).
Customary is from 1523.