"fleeing, likely to flee," 1630s, with -ous + Latin fugaci-, stem of fugax "apt to flee, timid, shy," figuratively "transitory, fleeting," from fugere "to flee" (see fugitive). Related: Fugaciously; fugaciousness; fugacity.
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."
late 14c., "one who flees, a runaway, a fugitive from justice, an outlaw," from fugitive (adj.). Old French fugitif also was used as a noun meaning "fugitive person," and Latin fugitivus (adj.) commonly also was used as a noun meaning "a runaway, fugitive slave, deserter."