Loose garment some initially laugh at (5)
I believe the answer is:
smock
'loose garment' is the definition.
(type of loose-fitting garment)
'some initially laugh at' is the wordplay.
'initially' indicates taking the first letters.
'laugh at' becomes 'mock'.
The first letter of 'some' is 's'.
's'+'mock'='SMOCK'
(Other definitions for smock that I've seen before include "artist's attire" , "Artist's, peasant's, overall" , "Artist's loose overall" , "Loose overall or dress" , "Loose dress or blouse" .)