awesome adj.

c. 1300, aue, "fear, terror, great reverence," earlier aghe, c. 1200, from a Scandinavian source, such as Old Norse agi "fright;" from Proto-Germanic *agiz- (source also of Old English ege "fear," Old High German agiso "fright, terror," Gothic agis "fear, anguish"), from PIE *agh-es- (source also of Greek akhos "pain, grief"), from root *agh- (1) "to be depressed, be afraid" (see ail).

The current sense of "dread mixed with admiration or veneration" is due to biblical use with reference to the Supreme Being. To stand in awe (early 15c.) originally was simply to stand awe.

Al engelond of him stod awe.

["The Lay of Havelok the Dane," c. 1300]

Awe-inspiring is recorded from 1814. 

word-forming element used in making adjectives from nouns or adjectives (and sometimes verbs) and meaning "tending to; causing; to a considerable degree," from Old English -sum, identical with some, from PIE root *sem- (1) "one; as one, together with." Cognate with Old Frisian -sum, German -sam, Old Norse -samr; also related to same.

"It usually indicates the possession of a considerable degree of the quality named: as mettlesome, full of mettle or spirit; gladsome, very glad or joyous" [Century Dictionary]. It is also, disguised, the ending in buxom. For the -some used with numbers (twosome, foursome, etc.), see -some (2).