Swoon (5)
I believe the answer is:
faint
'swoon' is the definition.
(I know that swoon can be written as faint)
This is all the clue.
(Other definitions for faint that I've seen before include "Barely perceptible" , "Swoon, pass out" , "dull" , "Swoon, lose consciousness" , "Pale - pass out" .)