A lieutenant with love for singer (4)
I believe the answer is:
alto
'singer' is the definition.
(type of singing voice)
'a lieutenant with love' is the wordplay.
'lieutenant' becomes 'lt' (abbreviation for lieutenant).
'with' means one lot of letters go next to another.
'love' becomes 'o' (love means zero in tennis).
'a'+'lt'+'o'='ALTO'
'for' is the link.
(Other definitions for alto that I've seen before include "Kind of singing voice, male or female" , "Key old > male who scores high" , "A singing voice or pitch" , "Male singer" , "Counter-tenor or contralto" .)