Bank mark breaks record (6)
I believe the answer is:
escarp
'bank' is the definition.
(thesaurus)
'mark breaks record' is the wordplay.
'mark' becomes 'scar' (synonyms).
'breaks' indicates putting letters inside.
'record' becomes 'ep'.
'scar' inserted inside 'ep' is 'ESCARP'.
(Other definitions for escarp that I've seen before include "Steep artificial slope in front of a fortification" , "part of fortification" , "Slope beneath rampart" , "Steep rise once" , "Inner side of ditch in fortifications" .)