Is it mostly borrowed from jargon? (5)
I believe the answer is:
argot
'jargon?' is the definition.
('argot' can be a synonym of 'jargon')
'is it mostly borrowed' is the wordplay.
I cannot really see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
The remaining letters 'argo' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'from' is the link.
Can you help me to learn more?
(Other definitions for argot that I've seen before include "Talk of thieves" , "manner of speaking" , "secret language" , "Jargon or slang (of a group)" , "Slang for a groat (5)" .)