Lower part of rigging cut from triangle, part of a ladder (7)
I believe the answer is:
ratline
I believe this is a quadruple definition!!
'lower part' is the first definition.
'ratline' can be an answer for 'part' (I have seen 'part of rigging' mean 'ratline' so perhaps 'part' could also mean 'ratline'). I am unsure of the 'lower' bit.
'of' is a link.
'rigging' is the second definition.
(thesaurus)
'cut from triangle' is the third definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'part of a ladder' is the fourth definition.
'ratline' can be an answer for 'part' (I have seen 'part of rigging' mean 'ratline' so perhaps 'part' could also mean 'ratline'). I'm not certain of the 'of a ladder' bit.
(Other definitions for ratline that I've seen before include "Rope forming part of steps on ship's rigging" , "Reliant (anag.)" , "Small rope for climbing on rigging" .)