Makes a terrible fuss at the right times (5)
I believe the answer is:
rages
'makes a terrible fuss' is the definition.
The answer and definition can be both to do with fundamental existence as well as being verbs in their -s form.
Perhaps there's an association between them I don't understand?
'at the right times' is the wordplay.
'at' is a charade indicator (letters next to each other).
'the right' becomes 'r' (common abbreviation).
'times' becomes 'ages' (age is a kind of time).
'r'+'ages' is 'RAGES'.
Can you help me to learn more?
(Other definitions for rages that I've seen before include "speaks as Hitler!" , "Fits of temper" , "becomes furious" , "gives anger vent" , "Passions" .)