A nail may be put up to secure a vine (5)
I believe the answer is:
liana
'a vine' is the definition.
(I know that Liana is a type of vine)
'a nail may be put up' is the wordplay.
'may be put up' says the letters should be written backwards (in a down clue, letters go up).
'a'+'nail'='anail'
'anail' backwards is 'LIANA'.
'to secure' is the link.
(Other definitions for liana that I've seen before include "Climbing-plant" , "Woody climbing tropical plant -- a nail (anag)" , "Climbing plant of rainforests" , "climber in the tropics" , "Woody forest climber" .)