Shanty about upright character joining navy salt? (9)
I believe the answer is:
seasoning
'salt?' is the definition.
(salt is a kind of seasoning)
'shanty about upright character joining navy' is the wordplay.
'shanty' becomes 'sea song' (a shanty is a sea song).
'about' means one lot of letters goes inside another.
'upright character' becomes 'I' (vertical letter of the alphabet).
'joining' is a charade indicator (letters next to each other).
'navy' becomes 'N' (common abbreviation eg in RN Royal Navy).
'i' after 'n' is 'ni'.
'seasong' enclosing 'ni' is 'SEASONING'.
(Other definitions for seasoning that I've seen before include "Add it to give flavour" , "Something added for flavour" , "Food flavouring" , "Could be salt" , "salt, for example" .)