Issue clear in poem (6)
I believe the answer is:
sonnet
'poem' is the definition.
(sonnet is a kind of poem)
'issue clear' is the wordplay.
'issue' becomes 'son' (issue can mean someone's offspring**).
'clear' becomes 'net' (as in net profit).
'son'+'net'='SONNET'
'in' acts as a link.
(Other definitions for sonnet that I've seen before include "Tonnes (anag.)" , "Poem of 14 lines - Shakespeare wrote lots" , "A form of poetry" , "14-line verse" , "Fourteen line poem" .)