Drone on about passable claptrap (5)
I believe the answer is:
hokum
'claptrap' is the definition.
(I've seen this in another clue)
'drone on about passable' is the wordplay.
'drone' becomes 'hum' (I've seen this before).
'on' is an insertion indicator (as in clothing 'on' a person).
'about passable' becomes 'ok' (I am not sure about the 'about' bit.).
'hum' going around 'ok' is 'HOKUM'.
Can you help me to learn more?
(Other definitions for hokum that I've seen before include "Meaninglessness" , "gammon" , "Sentimental stuff in play or film, nonsense" , "Rubbish" , "Be extremely good (at activity)" .)