Obstruct poet endlessly (3)
I believe the answer is:
bar
'obstruct' is the definition.
(barring is a kind of obstructing)
'poet endlessly' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'endlessly' means to remove the last letter.
'bard' with its last letter taken away is 'BAR'.
(Other definitions for bar that I've seen before include "Sandbank; pub counter" , "Inn" , "saving" , "whose moaning Tennyson hoped to prevent?" , "Shut out" .)