1. A device or substance that makes a certain thing taste, look, smell, or feel better: While cooking dinner, Jill added some garlic to the sauce as an enhancer to make it taste even better with the spaghetti!

Some new renovations in town certainly enhanced the attractiveness and encouraged more tourists to come and visit.
2. In genetics, a gene or gene fragment that activates other genes: An enhancer is a short amount of DNA that can improve the transcription of genes.