Nick, with your old-fashioned support, is unobtrusive (8)
I believe the answer is:
stealthy
'unobtrusive' is the definition.
(I've seen this before)
'nick with your old' is the wordplay.
'nick' becomes 'steal' (I've seen this before).
'with' means one lot of letters go next to another.
'your old' becomes 'thy' ('thy' historically meant 'your').
'steal'+'thy'='STEALTHY'
'fashioned support is' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for stealthy that I've seen before include "Underhand" , "That's Ely (anag.)" , "Moving surreptitiously" , "'Furtive, surreptitious (8)'" , "Unobtrusive" .)