Awful lapse is a bit of a bloomer (5)
I believe the answer is:
sepal
'a bit of a bloomer' is the definition.
(part of a flower)
'awful lapse' is the wordplay.
'awful' indicates anagramming the letters.
'lapse' is an anagram of 'SEPAL'.
'is' is the link.
(Other definitions for sepal that I've seen before include "flowery bit" , "Violet" , "bit of a bloomer" , "Part of a flower - peals (anag)" , "Part of the calyx of a flower" .)