About poems being secret writings (5)
I believe the answer is:
codes
'being secret writings' is the definition.
'about poems' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa').
'poems' becomes 'odes' (ode is a kind of poem).
'c'+'odes'='CODES'
(Other definitions for codes that I've seen before include "morals" , "Lots of laws" , "Word systems devised to create secrecy" , "Systems for transmitting secret messages" , "Symbolic systems" .)