Stops repressing one's annoyance, which is hazardous (9)
I believe the answer is:
endangers
'stops repressing one's annoyance which is hazardous' is the definition.
The definition and answer can be both to do with fundamental existence as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?
'stops repressing one's annoyance' is the wordplay.
'stops' becomes 'ends' ('end' can be a synonym of 'stop').
'repressing' means one lot of letters goes inside another.
'one's annoyance' becomes 'anger' (I can't justify this - if you can you should believe this answer much more).
'ends' enclosing 'anger' is 'ENDANGERS'.
Can you help me to learn more?
(Other definitions for endangers that I've seen before include "Puts in peril" , "Imperils" , "Puts into jeopardy" , "Risks" , "Placed in peril" .)