癇 is a bound form meaning 'temper' or 'irritability', often used in compounds like 癇が強い (short-tempered). 癇癪 is the more common standalone word for a tantrum.
Etymology
The kanji 癇 and 癪 both relate to illness or spasms, reflecting the historical view of tantrums as a kind of fit. The exact derivation is uncertain, but the word has been used since the Edo period.
