One's present part of course entertains Poles (5)
I believe the answer is:
tense
'one's present' is the definition.
(present tense is an example)
'part of course entertains poles' is the wordplay.
'part of course' becomes 'tee' (I've seen this before).
'entertains' means one lot of letters goes inside another.
'poles' becomes 'ns' (North and South poles).
'tee' going around 'ns' is 'TENSE'.
(Other definitions for tense that I've seen before include "Future, possibly" , "Uneasy" , "far from comfortable" , "It may be perfect" , "Present, possibly" .)