Slight strain's ultimately concealed (6)
I believe the answer is:
insult
'slight' is the definition.
(thesaurus)
'strain's ultimately concealed' is the wordplay.
'concealed' says the answer is hidden in the clue.
'INSULT' is hidden in the letters of 'strains ultimately'.
(Other definitions for insult that I've seen before include "Remark intended to hurt or humiliate" , "Abusive remark" , "An addition to injury?" , "Hurtful and offensive remark" , "Show contempt to" .)