Paid poet on regular basis for musical instrument (4)
I believe the answer is:
pipe
'musical instrument' is the definition.
(pipe is a kind of musical instrument)
'paid poet on regular basis' is the wordplay.
'on regular basis' means one should take alternating letters (letters selected at regular intervals).
'paid'+'poet'='paidpoet'
The alternating letters of 'paidpoet' are 'PIPE'.
'for' acts as a link.
(Other definitions for pipe that I've seen before include "Tube for conveying gas or liquid" , "Means of conveying" , "Water carrier" , "Tube, maybe musical" , "Meerschaum" .)