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 can't justify this - if you can you should believe this answer much more).
'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" .)