Bloomer made by union leader initially entering dump (5)
I believe the answer is:
tulip
'bloomer' is the definition.
(I've seen this before)
'union leader initially entering dump' is the wordplay.
'initially' suggests taking the first letters.
'entering' is an insertion indicator.
'dump' becomes 'tip' (as in a rubbish tip).
The initial letters of 'union leader' is 'ul'.
'ul' going into 'tip' is 'TULIP'.
'made by' is the link.
(Other definitions for tulip that I've seen before include "Bulbous plant" , "Garden flower from bulb" , "Spring-blooming plant" , "Spring-flowering plant" , "(Dutch) bloom" .)