Simple poem in manuscript ending in basket (6)
I believe the answer is:
modest
'simple' is the definition.
(similar in meaning)
'poem in manuscript ending in basket' is the wordplay.
'poem' becomes 'ode' (ode is a kind of poem).
'in' indicates putting letters inside.
'manuscript' becomes 'ms' (abbreviation for manuscript).
'ending in' indicates one should take the final letters.
The final letter of 'basket' is 't'.
'ode' put inside 'ms' is 'modes'.
'modes'+'t'='MODEST'
(Other definitions for modest that I've seen before include "Not vain or showy" , "retiring" , "Mussorgsky, nominally?" , "self-effacing" , "Decorous" .)