Some coastguard entirely zealous (6)
I believe the answer is:
ardent
'zealous' is the definition.
(synonyms)
'some coastguard entirely' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ARDENT' is hidden in the letters of 'coastguard entirely'.
(Other definitions for ardent that I've seen before include "Warm and loving" , "Intensely devoted" , "Passionate, fervent" , "passion" , "Enthusiastic, eager" .)