This type of thing must fall (5)
I believe the answer is:
night
'must fall' is the definition.
The answer and definition can be both related to time as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'this type of thing' is the wordplay.
'this type of' indicates anagramming the letters (I've seen 'type' mean this).
'thing' is an anagram of 'NIGHT'.
Can you help me to learn more?
(Other definitions for night that I've seen before include "Period of darkness" , "See 1 Across" , "Evening" , "Ignorance" , "Illumination needed now" .)