petulant adj.

Also petə-, Proto-Indo-European root meaning "to rush, to fly." 

It forms all or part of: accipiter; appetence; appetite; apterous; apteryx; archaeopteryx; asymptote; centripetal; Coleoptera; compete; competent; eurypterid; feather; helicopter; hippopotamus; Hymenoptera; impetigo; impetuous; impetus; iopterous; Lepidoptera; ornithopter; panache; panne; pen (n.1) "writing implement;" pennon; peripeteia; perpetual; perpetuity; petition; petulance; petulant; pin; pinion; pinnacle; pinnate; pinniped; potamo-; potamology; propitiation; propitious; ptero-; pterodactyl; ptomaine; ptosis; repeat; symptom.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit pattram "wing, feather, leaf," patara- "flying, fleeting;" Hittite pittar "wing;" Greek piptein "to fall," potamos "river, rushing water," pteron, pteryx "feather, wing," ptilon "soft feathers, down, plume;" Latin petere "to attack, assail; seek, strive after; ask for, beg; demand, require," penna "feather, wing;" Old Norse fjöðr, Old English feðer "feather;" Old Church Slavonic pero "feather;" Old Welsh eterin "bird."

"fit of peevishness, offense or ill-humor at feeling slighted," 1580s, in phrase take the pet "take offense." Perhaps from pet (n.1) on a similar notion to that in American English that gets my goat (for which see goat), but the underlying notion is obscure, and the form of the original expression makes this doubtful. Perhaps from the notion of "characteristic of an indulged or spoiled child," but OED notes that this word seems to have been originally a southern English term, while pet (n.1) was northern and Scottish. Perhaps influenced by unrelated petulant.

c. 1600, "insolence, immodesty, rudeness," from French pétulance (early 16c.), from Latin petulantia "sauciness, impudence," abstract noun from petulantem (see petulant). Meaning "peevishness" is recorded by 1784, from influence of pettish, etc. It displaced earlier petulancy (1550s in the first sense, 1712 in the second).