The stuff had cooled and jelled into a half-solid condition.
But in five or six years after, when your character has jelled, and you've hit your pace, you'll bless me for it.
1830, American English, probably a back-formation of jelly (v.). Related: Jelled; jelling. Figurative sense is first attested 1908. Middle English had gelen "congeal," but it disappeared 15c.