Trained gymnast must keep tense (4)
I believe the answer is:
'tense' is the definition.
(similar in meaning)
'trained gymnast must keep' is the wordplay.
'keep' says the answer is hidden in the clue.
'EDGY' is hidden within 'trained gymnast must'.
(Other definitions for edgy that I've seen before include "Extremely" , "Apprehensive" , "Nervous and tense, irritable" , "Uneasy" , "Anxious" .)