Saint has garment, something flashy (6)
I believe the answer is:
strobe
'something flashy' is the definition.
(strobe light)
'saint has garment' is the wordplay.
'saint' becomes 'st' (abbreviation).
'has' means one lot of letters go next to another.
'garment' becomes 'robe' (robe is a type of garment).
'st'+'robe'='STROBE'
(Other definitions for strobe that I've seen before include "Light that seems to spin" , "Flashing lamp" , "Sorbet (anag) -flashing light" , "Rapidly flashing lighting often used on stage" , "Flashy type" .)