arch-1

1.
a combining form that represents the outcome of archi- in words borrowed through Latin from Greek in the Old English period; it subsequently became a productive form added to nouns of any origin, which thus denote individuals or institutions directing or having authority over others of their class (archbishop; archdiocese; archpriest). More recently, arch-1, has developed the senses “principal” (archenemy; archrival) or “prototypical” and thus exemplary or extreme (archconservative); nouns so formed are almost always pejorative.
Origin
Middle English; Old English arce-, ærce-, erce- (> Old Norse erki-) < Latin archi- < Greek (see archi-); but Dutch aarts-, Middle Low German erse-, Middle High German, German Erz- < Medieval Latin arci-, and Gothic ark- directly < Greek. Cf. archangel

arch-2

1.
variant of archi- before a vowel:
archangel; archenteron.
British Dictionary definitions for arch-

arch-

combining form
1.
chief; principal; of highest rank: archangel, archbishop, archduke
2.
eminent above all others of the same kind; extreme: archenemy, archfiend, archfool
Word Origin
ultimately from Greek arkhi-, from arkhein to rule
Word Origin and History for arch-

also archi-, word-forming element meaning "chief, principal; extreme, ultra; early, primitive," from Latinized form of Greek arkh-, arkhi- "first, chief, primeval," comb. form of arkhos "chief" (see archon).