"amorous trifling; giddy behavior," 1718, noun of action from flirt (v.) as though Latin. The date, alas, gives the lie to Chesterfield's charming story of its coinage (in The World, Dec. 5, 1754) but not his refinement of the definition: "[F]lirtation is short of coquetry, and intimates only the first hints of approximation, which subsequent coquetry may reduce to those preliminary articles, that commonly end in a definitive treaty."
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."
<a href="https://www.etymonline.com/word/flirtatious">Etymology of flirtatious by etymonline</a>
Harper, D. (n.d.). Etymology of flirtatious. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/flirtatious