fitful adj.

"paroxysm, sudden attack" (as of anger), 1540s, probably via Middle English sense of "painful, exciting experience" (early 14c.), from Old English fitt "conflict, struggle," which is of uncertain origin, with no clear cognates outside English. Perhaps ultimately cognate with fit (adj.) on notion of "to meet." Meaning "sudden impulse toward activity or effort" is from 1580s. Phrase by fits and starts first attested 1610s (by fits is from 1580s).

word-forming element attached to nouns (and in modern English to verb stems) and meaning "full of, having, characterized by," also "amount or volume contained" (handful, bellyful); from Old English -full, -ful, which is full (adj.) become a suffix by being coalesced with a preceding noun, but originally a separate word. Cognate with German -voll, Old Norse -fullr, Danish -fuld. Most English -ful adjectives at one time or another had both passive ("full of x") and active ("causing x; full of occasion for x") senses.

It is rare in Old English and Middle English, where full was much more commonly attached at the head of a word (for example Old English fulbrecan "to violate," fulslean "to kill outright," fulripod "mature;" Middle English had ful-comen "attain (a state), realize (a truth)," ful-lasting "durability," ful-thriven "complete, perfect," etc.).