Merely, purely, barely (4,4)

I believe the answer is:

only just

'barely' is the definition.
(thesaurus)

'merely purely' is the wordplay.
'merely' becomes 'only' (synonyms).
'purely' becomes 'just' (just can mean purely or simply).
'only'+'just'='ONLY JUST'

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app