late 14c., "conflict, fighting; difficulty, trouble," a contraction of at do, literally "to do," a dialectal northern English formation in the Norse-influenced areas of England, as some Scandinavian languages used at with the infinitive of a verb where Modern English uses to. From use of the infinitive in much ado ("much to do") and similar phrases, ado came to be regarded as a noun. Compare the sense evolution in to-do and affair (from French infinitive phrase à faire "to do"). The weakened meaning "fuss" is from early 15c. Also used in Middle English for "dealings, traffic," and "sexual intercourse" (both c. 1400).