Release group gratis (3,4)

I believe the answer is:

set free

'release' is the definition.
(synonyms)

'group gratis' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'gratis' becomes 'free' (synonyms).
'set'+'free'='SET FREE'

(Other definitions for set free that I've seen before include "no longer detained" , "Liberate" , "Release, remove restraints" , "Clear" , "no longer confined" .)

I've seen this clue in the Sydney Morning Herald.

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