At first look daggers at a bloomer (7)
I believe the answer is:
lobelia
'bloomer' is the definition.
(blooming flower)
'at first look daggers at a' is the wordplay.
'at' says to put letters next to each other.
'first look' becomes 'l' (1st letter of 'look').
'daggers' becomes 'obeli' (I've seen this before).
'at' says to put letters next to each other.
'l' next to 'obeli' is 'lobeli'.
'lobeli'+'a'='LOBELIA'
(Other definitions for lobelia that I've seen before include "Showy garden flower" , "Five-lobed flower" , "Oil bale (anag) - flower" , "Tropical or subtropical bedding plant" , "something flowery" .)