From Middle English sponeful, sponefull, sponful, spone-ful, equivalent to spoon + -ful.
spoonful (plural spoonfuls or spoonsful)
- The amount that a spoon will hold, either level or heaped.
1959, Georgette Heyer, chapter 1, in The Unknown Ajax:
But Richmond […] appeared to lose himself in his own reflections. Some pickled crab, which he had not touched, had been removed with a damson pie; and his sister saw […] that he had eaten no more than a spoonful of that either.