someone's word is law

: some person : somebody

: something that is said

: talk, discourse

: the text of a vocal musical composition

: speak

: to express in words : phrase

: a binding custom or practice of a community : a rule of conduct or action prescribed (see prescribe 1a) or formally recognized as binding or enforced by a controlling authority

: the whole body of such customs, practices, or rules

: common law

: litigate

: to sue or prosecute at law