Gentle exercises with expert virtually complete (8)
I believe the answer is:
peaceful
'gentle' is the definition.
(thesaurus)
'exercises with expert virtually complete' is the wordplay.
'exercises' becomes 'pe' (Physical Education).
'with' means one lot of letters go next to another.
'expert' becomes 'ace' (ace can informally mean very good).
'virtually' means to remove the last letter (virtually all of the word, but not the last letter).
'complete' becomes 'full' (similar in meaning).
'full' with its final letter removed is 'ful'.
'pe'+'ace'+'ful'='PEACEFUL'
(Other definitions for peaceful that I've seen before include "Not violent" , "Tranquil, calm" , "Not disturbed by strife or war" , "Quiet" , "Placid, not belligerent" .)