The Oxford Thesaurus An A-Z Dictionary of Synonyms - archadj.

1) chief, principal, prime, primary, pre-eminent, foremost, first, greatest, consummate, major: Moriarty was Holmes's arch-enemy. 2) clever, cunning, crafty, roguish, tricky, shrewd, artful, sly, designing: Brendan loves to play his arch pranks on unsuspecting friends. 3) waggish, saucy, mischievous, prankish: I could tell from the lad's arch expression that he had thrown the snowball.