A wave from the Queen on holiday? (7)
I believe the answer is:
breaker
'a wave' is the definition.
(breaker is a kind of wave)
'the queen on holiday?' is the wordplay.
'the queen' becomes 'er' (Elizabeth Regina).
'on' means one lot of letters go next to another.
'holiday?' becomes 'break' (I've seen this before).
'er' put after 'break' is 'BREAKER'.
'from' acts as a link.
(Other definitions for breaker that I've seen before include "User of CB radio" , "Wave hitting the shore" , "A large wave, sounds destructive" , "Large sea wave" , "Roller?" .)