For party it's serious when leader is deposed (4)
I believe the answer is:
rave
'for party' is the definition.
(type of dance party)
'it's serious when leader is deposed' is the wordplay.
I cannot quite see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
The remaining letters 'rav' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rave that I've seen before include "Enthusiastically favourable review" , "Enthuse; rant" , "Rapturous" , "Rant - noisy, all-night party" , "Talk incoherently" .)