Distress developed into a gait (9)
I believe the answer is:
agitation
'distress' is the definition.
(thesaurus)
'developed into a gait' is the wordplay.
'developed' indicates an anagram.
'into'+'a'+'gait'='intoagait'
'intoagait' is an anagram of 'AGITATION'.
(Other definitions for agitation that I've seen before include "State of nervous excitement" , "disquiet" , "Disturbance, excitation" , "Nervous anxiety" , "Nervousness" .)