A measure of whisky not opened? It's on the house (4)
I believe the answer is:
roof
'it's on the house' is the definition.
(I've seen this in another clue)
'a measure of whisky not opened?' is the wordplay.
I cannot really understand how this works, but
'measure' could be 'r' (R is an example) and 'r' is found within the answer.
'of' could be 'o' and 'o' is found in the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
A single letter 'f' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for roof that I've seen before include "Canopy" , "House's top" , "Mansard is an example of one" , "One is angry when one hits it" , "hit by someone in a temper" .)