First husband has terrible tan fixed (7)
I believe the answer is:
adamant
'fixed' is the definition.
(both can mean determined or unwavering)
'first husband has terrible tan' is the wordplay.
'first husband' becomes 'adam' (Adam was Eve's husband in the Garden of Eden).
'has' means one lot of letters go next to another.
'terrible' is an anagram indicator.
'tan' is an anagram of 'ant'.
'adam'+'ant'='ADAMANT'
(Other definitions for adamant that I've seen before include "uncompromising" , "Inexorable" , "Hard stone" , "Inflexible, obdurate" , "Firm and unyielding" .)