teaspoonful

Concise Oxford English Dictionary © 2008 Oxford University Press:
teaspoon/ˈtiːspuːn/

▶noun a small spoon used for adding sugar to and stirring hot drinks.

■ (abbrev.: tsp) the amount held by a teaspoon, in the UK considered to be 5 millilitres when used as a measurement in cookery.

– derivatives
teaspoonful noun (pl. teaspoonfuls).