Mean to be secure (5)
I believe the answer is:
tight
This clue is a double definition.
'mean' is the first definition.
(synonyms)
'be secure' is the second definition.
(similar in meaning)
'to' acts as a link.
(Other definitions for tight that I've seen before include "Firmly fastened; tense" , "Close-fitting; drunk" , "Miserly or blotto" , "with limited room to manoeuvre" , "Close-fitting; cramped; mean" .)