Unpretentious metre: poem is on the way (6)
I believe the answer is:
modest
'unpretentious' is the definition.
('modest' can be similar in meaning to 'unpretentious')
'metre poem is on the way' is the wordplay.
'metre' becomes 'm' ('m' can be a synonym of 'metre').
'poem' becomes 'ode' (ode is a kind of poem**).
'is on' is a charade indicator (letters next to each other).
'the way' becomes 'st'.
'm'+'ode'+'st'='MODEST'
(Other definitions for modest that I've seen before include "Humble, unpretentious" , "Not excessive in rating one's own achievements" , "Avoiding indecency; unassuming" , "'Humble, unassuming (6)'" , "Prudent" .)