Chapter in English constitutes poetic lines on page (7)
I believe the answer is:
episode
'chapter' is the definition.
(I've seen this in another clue)
'english constitutes poetic lines on page' is the wordplay.
'english' becomes 'E' (abbreviation).
'constitutes' becomes 'is' ('be' can be a synonym of 'constitute').
'poetic lines' becomes 'ode' (lines of poetry. I am not sure about the 'poetic' bit.).
'on' says to put letters next to each other.
'page' becomes 'p'.
'is'+'ode'='isode'
'isode' put after 'p' is 'pisode'.
'e'+'pisode'='EPISODE'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for episode that I've seen before include "One part of a serial" , "Instalment of broadcast serial" , "One programme of a series" , "Incident forming part of a sequence" , "One part of a series" .)