Way, way humble (6)
I believe the answer is:
modest
'humble' is the definition.
('modest' can be a synonym of 'humble')
'way way' is the wordplay.
'way' becomes 'mode' ('mode' can be a synonym of 'way'**).
'way' becomes 'st'.
'mode'+'st'='MODEST'
(Other definitions for modest that I've seen before include "Simple, humble" , "Not excessive in rating one's own achievements" , "Unostentatious" , "Not vain or showy" , "Humble, not pretentious or showy" .)