About to relax and fizzle out (5)
I believe the answer is:
cease
'fizzle out' is the definition.
The definition and answer can be both to do with fundamental existence as well as being verbs in their base form.
Maybe you can see a link between them that I don't see?
'about to relax' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'to relax' becomes 'ease' (eg to ease a restriction is to relax it).
'c'+'ease'='CEASE'
'and' is the link.
Can you help me to learn more?
(Other definitions for cease that I've seen before include "Desist" , "Come to an end" , "Stop, terminate" , "Stop, finish" , "Discontinue" .)