American Heritage® Dictionary of the English Language, Fourth Edition
- n. The amount that a teacup can hold.
Century Dictionary and Cyclopedia
- n. As much as a tea-cup will hold; as a definite quantity, four fluidounces, or one gill.
GNU Webster's 1913
- n. As much as a teacup can hold; enough to fill a teacup.
- n. as much as a teacup will hold
- teacup + -ful (Wiktionary)
“Boil a teacupful of tea in three pints of water for ten minutes with a heaped dessert-spoonful of soda.”
“I suppose he must have used quite a teacupful of olive oil.”
““We had literally only a teacupful of water each day to wash in,” Jean said, which was “quite a hardship when we were covered from head to foot in white dust by the end of the day.””
“Winston poured out nearly a teacupful, nerved himself for a shock, and gulped it down like a dose of medicine.”
“He went into the kitchen and swallowed nearly a teacupful of Victory Gin.”
“Similarly, if an ounce of the bruised root is boiled in three half-pints of water, down to a pint, a teacupful of this may be given every three or four hours.”
“A teaspoonful of these buds is ordered to be infused in a teacupful of quite hot water, and the liquid to be drunk shortly, before going to bed.”
“By pouring a pint of boiling water on a handful of the plant -- stems, flowers and leaves -- an  excellent gargle may be made for a relaxed throat; and a teacupful of the same infusion may be taken cold three or four times in the day for simple looseness of the bowels; also for passive losses of blood.”
“For obstinate hiccough a teacupful of boiling water should be poured on a teaspoonful of Mustard flour, and taken when sufficiently cool, half at first, and the other half in ten minutes if still needed.”
“If the leaves are gathered in the Spring and dried, then, when required, a handful of them may be infused in a pint of boiling water, and the infusion, when cool, may be taken, a teacupful at a time, to stay diarrhoea, and for some bleedings.”
These user-created lists contain the word ‘teacupful’.
I'm especially fond of ones written by Charles Sanders Peirce.
Looking for tweets for teacupful.