Measure a little drop in teaspoon (4)
I believe the answer is:
pint
'measure' is the definition.
(pint is a kind of measure)
'a little drop in teaspoon' is the wordplay.
'a little' indicates the answer is hidden within the clue (a little bit of the clue).
'PINT' can be found hidden inside 'drop in teaspoon'.
(Other definitions for pint that I've seen before include "The working man's beer measure" , "Half a quart" , "One eighth of a gallon" , "Imperial measure of capacity" , "Liquid meassure - four gills" .)