Term is used to call a man (6)
I believe the answer is:
mister
'call a man' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'term is used' is the wordplay.
'used' indicates anagramming the letters.
'term'+'is'='termis'
'termis' is an anagram of 'MISTER'.
'to' is the link.
Can you help me to learn more?
(Other definitions for mister that I've seen before include "Form of address to a man, used without his name" , "Male form of address" , "Merits of form of address to man" , "Mr" , "Set rim (anag.)" .)