Cut off part of hanging cloth — mostly length (7)
I believe the answer is:
curtail
'cut off' is the definition.
(thesaurus)
'hanging cloth mostly length' is the wordplay.
'hanging cloth' becomes 'curtain' (I've seen this before).
'mostly' means to remove the last letter (most but not all of the word).
'length' becomes 'l' (abbreviation in geometry).
'curtain' with its last letter removed is 'curtai'.
'curtai'+'l'='CURTAIL'
'part of' is the link.
(Other definitions for curtail that I've seen before include "Abbreviate" , "'Cut short, restrict (7)'" , "Shorten, abridge" , "Dock" , "make shorter" .)