Break cover say with REME retreating (6)
I believe the answer is:
emerge
'break cover' is the definition.
(thesaurus)
'say with reme retreating' is the wordplay.
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'with' says to put letters next to each other.
'retreating' says the letters should be written backwards.
'eg'+'reme'='egreme'
'egreme' backwards is 'EMERGE'.
(Other definitions for emerge that I've seen before include "Issue" , "Break out (from an egg)" , "Come into view" , "Come out or surface" , "(Of facts) become known" .)