Rants about poetry, cross (10)
I believe the answer is:
transverse
'cross' is the definition.
(transverse means cross or across)
'rants about poetry' is the wordplay.
'about' indicates an anagram.
'poetry' becomes 'verse' (lines written in verse).
'rants' is an anagram of 'trans'.
'trans'+'verse'='TRANSVERSE'
(Other definitions for transverse that I've seen before include "Crossing" , "Extending across something" , "Situated across something" , "Extending across (the long axis)" , "Crosswise" .)