It's a decorative edging one gathers (5)
I believe the answer is:
frill
'edging one gathers' is the definition.
'frill' can be an answer for 'edging' (I have seen 'Ornamental edging' mean 'frill' so perhaps 'edging' could also mean 'frill'). I'm not certain of the 'one gathers' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for frill that I've seen before include "Gathered strip as a trimming" , "Trim" , "Pleated strip of cloth trimming or an unnecessary extra" , "A decorative gathering of fabric" , "Gathered material" .)