Enlargement of fashionable pleat? (8)
I believe the answer is:
increase
'enlargement' is the definition.
(thesaurus)
'fashionable pleat?' is the wordplay.
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'pleat?' becomes 'crease' (crease in a skirt).
'in'+'crease'='INCREASE'
'of' is the link.
(Other definitions for increase that I've seen before include "'Augment, expand (8)'" , "Grow, expand" , "Become greater in number" , "Addition, growth" , "Get bigger" .)