Chaucer's first poems, which need deciphering (5)
I believe the answer is:
codes
'which need deciphering' is the definition.
(codes must be deciphered)
'chaucer's first poems' is the wordplay.
'chaucer's first' becomes 'c' (1st letter of 'chaucer').
'poems' becomes 'odes' (ode is a kind of poem).
'c'+'odes'='CODES'
(Other definitions for codes that I've seen before include "Sets of rules or cryptograms" , "System of letters etc for the purpose of secrecy" , "Word systems devised to create secrecy" , "Symbolic systems" , "morals" .)