Second blast outside is very close (5)
I believe the answer is:
bosom
'very close' is the definition.
(as in bosom friends, very close friends)
'second blast outside' is the wordplay.
'second' becomes 's' (common abbreviation).
'blast' becomes 'boom' (synonyms).
'outside' indicates putting letters inside.
's' put inside 'boom' is 'BOSOM'.
'is' is the link.
(Other definitions for bosom that I've seen before include "Woman's breast" , "heart of family" , "(Female's) chest" , "Embrace" , "Breast, chest" .)