Spun length of cotton fibre otherwise (2,3)
I believe the answer is:
if not
'otherwise' is the definition.
(synonyms)
'spun length of cotton fibre' is the wordplay.
'IF NOT' is hidden backwards in amongst the letters.
However, I am uncertain how the hidden word is indicated.
Can you help me to learn more?
(Other definitions for if not that I've seen before include "Unless" , "Failing that" .)