Mark covering American bear (7)
I believe the answer is:
sustain
'bear' is the definition.
(thesaurus)
'mark covering american' is the wordplay.
'mark' becomes 'stain' ('stain' can be a synonym of 'mark'**).
'covering' indicates putting letters inside.
'american' becomes 'us'.
'stain' placed around 'us' is 'SUSTAIN'.
(Other definitions for sustain that I've seen before include "Keep alive" , "Strengthen physically" , "Endure" , "Maintain" , "Nurish" .)