Longman Dictionary of Contemporary English
The Collaborative International Dictionary
Arch- \Arch-\ (["a]rch-, except in archangel and one or two other words). [L. arch-, Gr. 'arch- = 'archi-. See Arch-.] A prefix signifying chief, as in archbuilder, archfiend.
Douglas Harper's Etymology Dictionary
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).
Wiktionary
pre. chief, highest, most extreme
Usage examples of "arch-".
Nature of the circumnutating movement--History of a germinating seed--The radicle first protrudes and circumnutates--Its tip highly sensitive--Emergence of the hypocotyl or of the epicotyl from the ground under the form of an arch--Its circumnutation and that of the cotyledons--The seedling throws up a leafbearing stem--The circumnutation of all the parts or organs--Modified circumnutation--Epinasty and hyponasty--Movements of climbing plants--Nyctitropic movements--Movements excited by light and gravitation--Localised sensitiveness--Resemblance between the movements of plants and animals--The tip of the radicle acts like a brain.