A set of lines as form of transport (8)
I believe the answer is:
quatrain
'a set of lines' is the definition.
'quatrain' can be an answer for 'lines' (I have seen 'poetic lines' mean 'quatrain' so perhaps 'lines' could also mean 'quatrain'). I am not sure about the 'a set of' bit.
'as form of transport' is the wordplay.
'as' becomes 'qua' (I've seen this before).
'form of transport' becomes 'train' (I've seen this before).
'qua'+'train'='QUATRAIN'
Can you help me to learn more?
(Other definitions for quatrain that I've seen before include "Four-line stanza" , "Stanza or poem of four lines" , "Poem of four lines found in a quart" , "Poet may write it" , "Type of verse with four lines" .)