Unassuming, self-effacing (6)
I believe the answer is:
modest
This clue is a double definition.
'unassuming' is the first definition.
(similar in meaning)
'self-effacing' is the second definition.
(I've seen this before)
(Other definitions for modest that I've seen before include "Decorous" , "Not conceited, unassuming" , "Not having or showing pride" , "Unassuming; small" , "Unassuming or decent" .)