Most gentle (7)
'most gentle' is the definition.
('mild' can be similar in meaning to 'gentle')
This is the entire clue.
(Other definitions for mildest that I've seen before include "Most gentle" , "calmer than all the others" .)
(Other definitions for meekest that I've seen before include "Most humble" , "Most deferential" , "Most modest, humblest" .)