1. also re·press·er One that represses.
2. Genetics. A protein that binds to an operator, blocking transcription of an operon and the enzymes for which the operon codes.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.