arch (adj.)
chief, principal, pre-eminent
3H6 II.ii.2[Queen to King, of York] Yonder's the head of that arch-enemy / That sought to be encompassed with your crown
R3 IV.iii.2[Tyrrel alone, of killing the Princes] The most arch deed of piteous massacre [i.e. heinous deed]
SHAKESPEARE'S WORDS © 2018 DAVID CRYSTAL & BEN CRYSTAL