Speak slowly, line getting to drag on (5)
I believe the answer is:
drawl
'speak slowly' is the definition.
(I've seen this before)
'line getting to drag on' is the wordplay.
'line getting' becomes 'l' (I can't justify this - if you can you should give a lot more credence to this answer).
'to drag' becomes 'draw' ('draw' can be a synonym of 'drag').
'on' is a charade indicator (letters next to each other).
'l' put after 'draw' is 'DRAWL'.
(Other definitions for drawl that I've seen before include "Way of speaking slowly" , "Jimmy Stewart spoke with one" , "Speak slowly with long vowels sounds" , "Speak slowly and lazily" , "Prolong vowel sounds" .)