One blooming bunch, crossworders (5)
I believe the answer is:
lotus
'one blooming' is the definition.
(I have seen 'A blooming' mean 'lotus' so perhaps 'blooming' could also mean 'lotus')
'bunch crossworders' is the wordplay.
'bunch' becomes 'lot' (synonyms).
'crossworders' becomes 'us' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lot'+'us'='LOTUS'
Can you help me to learn more?
(Other definitions for lotus that I've seen before include "F1 team and car maker" , "Water-lily; yoga position" , "Sacred Egyptian water lily" , "Water lily - fruit inducing forgetfulness" , "Mythical fruit inducing state of luxurious dreaminess" .)