Coffee mug upended by daughter (5)
I believe the answer is:
decaf
'coffee' is the definition.
(type of coffee)
'mug upended by daughter' is the wordplay.
'mug' becomes 'face' (I've seen this in another clue).
'upended' says the letters should be written backwards (in a down clue, letters go up).
'by' means one lot of letters go next to another.
'daughter' becomes 'd' (genealogical abbreviation).
'face' written backwards gives 'ecaf'.
'ecaf' after 'd' is 'DECAF'.
(Other definitions for decaf that I've seen before include "Type of coffee" , "Coffee without the kick?" , "Cup substitute missing kick" , "Non-alcoholic drink" , "Style of coffee" .)