About poems being in secret languages (5)
I believe the answer is:
codes
'secret languages' is the definition.
(I've seen this in another clue)
'about poems' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'poems' becomes 'odes' (ode is a kind of poem).
'c'+'odes'='CODES'
'being in' is the link.
(Other definitions for codes that I've seen before include "Ciphers" , "Word systems devised to create secrecy" , "Sets of rules or cryptograms" , "System of letters etc for the purpose of secrecy" , "morals" .)