Sudden increase in twilled fabric, we hear (5)
I believe the answer is:
surge
'sudden increase' is the definition.
(a surge is a sudden increase in something)
'twilled fabric we hear' is the wordplay.
'twilled fabric' becomes 'serge' (type of fabric).
'we hear' indicates a 'sounds like' (homophone) clue.
'serge' is a homophone of 'SURGE'.
'in' acts as a link.
(Other definitions for surge that I've seen before include "Sudden rush" , "Rise suddenly" , "Sudden upward movement" , "Rise rapidly" , "Jerk" .)