Humdrum bedroom activity (7)
I believe the answer is:
boredom
'humdrum bedroom activity' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'bedroom activity' is the wordplay.
'activity' is an anagram indicator (letters become active).
'bedroom' is an anagram of 'BOREDOM'.
Can you help me to learn more?
(Other definitions for boredom that I've seen before include "Tedium, ennui" , "Ennui in bedroom" , "Overseers" , "Monotony" , "no interest" .)