Relaxing exercises with expert not quite complete (8)
I believe the answer is:
peaceful
'relaxing' is the definition.
(thesaurus)
'exercises with expert not quite complete' is the wordplay.
'exercises' becomes 'pe' (Physical Education class).
'with' says to put letters next to each other.
'expert' becomes 'ace' (ace can informally mean very good).
'not quite' means to remove the last letter.
'complete' becomes 'full' (similar in meaning).
'full' with its last letter removed is 'ful'.
'pe'+'ace'+'ful'='PEACEFUL'
(Other definitions for peaceful that I've seen before include "Calm and undisturbed by strife" , "Tranquil, calm" , "Serene" , "Placid, not belligerent" , "Amicable" .)