A really quiet ramble is OK (7)
I believe the answer is:
approve
'is ok' is the definition.
(to OK something is to approve it)
'a really quiet ramble' is the wordplay.
'really quiet' becomes 'pp' (musical abbreviation for pianissimo, 'very soft').
'ramble' becomes 'rove' (synonyms).
'a'+'pp'+'rove'='APPROVE'
(Other definitions for approve that I've seen before include "Officially accept as satisfactory" , "Confirm" , "Commend, endorse" , "Regard with favour" , "Think well of; sanction" .)