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' says to put letters next to each other.
'daughter' becomes 'd' (genealogical abbreviation).
'face' backwards is 'ecaf'.
'ecaf' put 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" .)