From Longman Dictionary of Contemporary Englishlonerlon‧er /ˈləʊnə $ ˈloʊnər/ noun [countable] ALONEsomeone who prefers to be alone or who has no friends Ken’s always been a bit of a loner.
Examples from the Corpus
loner• I see myself as a loner.• I had always been a loner, and I hated sharing an apartment when I went to college.• Each of these people is, like Carr, a loner who is quite at home with himself.• Mikhail Vologsky was essentially a loner, in both the physical and spiritual sense.• Joe is one of our best workers but he's too much of a loner to be a good leader.• Since the youths learn to hide their sexually deviant behavior, they tend to be loners.• Peaceful and lively, the fish is best in small shoals because loners or pairs become nervous.• If one can not, one gets a deluded loner nursing a dummy.• Nixon, the loner, was a workhorse with determination. 