An adjective that sounds a little like what it means, fitful means stopping and starting, on-again off-again, switching suddenly. I had a fitful night's sleep: I woke up several times throughout the night.

A fit is a disturbance that happens without warning, like a tantrum, tremor, or spasm. If something is fitful, it's "full of fits." A night at the opera is a night of fitful pleasures: the arias are cool, but the rest of the show is boring. I've made only fitful progress trying to lose weight, because I lose only a few pounds at a time, and they almost always come right back: my progress is fitful because it comes in "fits and starts."

Definitions of fitful

adj occurring in spells and often abruptly

fitful bursts of energy”
recurring in scattered and irregular or unpredictable instances

adj intermittently stopping and starting

fitful (or interrupted) sleep”
interrupted, off-and-on
not continuous in space, time, or sequence or varying abruptly

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