A frivolous school head comes to rest (7)
I believe the answer is:
alights
'comes to rest' is the definition.
(I've seen this in another clue)
'a frivolous school head' is the wordplay.
'frivolous' becomes 'light' (light can mean trivial or unimportant).
'head' suggests taking the first letters.
The initial letter of 'school' is 's'.
'a'+'light'+'s'='ALIGHTS'
(Other definitions for alights that I've seen before include "Lands" , "Comes down or dismounts" , "Comes to land" , "Gets down from, bus or train" , "Settles" .)