consuetude (n.)

late 14c., "custom, usage," from Old French consuetude and directly from Latin consuetudo "a being accustomed, habit, usage," from consuetus, past participle of consuescere "to accustom," from assimilated form of com-, here perhaps an intensive prefix (see com-), + suescere "become used to, accustom oneself," related to suus "oneself" (from PIE *swe- "oneself;" see idiom).

Meaning "that which one is accustomed to, habitual association" is from 1803. Related: Consuetudinal; consuetudinary.