A likeness is a QUALITY of being similar. I bear a likeness to my mother = we look similar. It can also be an OBJECT such as a painting, drawing, statue - something intended to look like somebody. I don't think the latest portrait of the Queen is a good likeness of her. A lookalike is a PERSON who looks very like another. Some people who resemble celebrities work as professional lookalikes. We hired some celebrity lookalikes for the party.