Strengthen, support (7)

I think it could be either:

bolster

sustain

I believe this clue is a double definition.

'strengthen' is the first definition.
(thesaurus)

'support' is the second definition.
(synonyms)

(Other definitions for sustain that I've seen before include "Withstand" , "Bear, hold, up" , "Carry" , "Endure" , "Support, keep going" .)

I've seen this clue in The Mirror and The Times.

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