Exercised, being intermittently unsteady (4)
I believe the answer is:
used
'exercised' is the definition.
(thesaurus)
'intermittently unsteady' is the wordplay.
'intermittently' indicates alternate letters.
The alternating letters of 'unsteady' are 'USED'.
'being' is the link.
(Other definitions for used that I've seen before include "No longer pristine" , "Availed oneself of" , "Employed - exploited" , "with some traffic" , "no stranger" .)