custom Look up custom at Dictionary.com
c.1200, "habitual practice," from O.Fr. costume, from V.L. *consuetumen, from L. consuetudinem (nom. 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. şeaw. Sense of a "regular" toll or tax on goods is early 14c.