To make or become thick or thicker: Thicken the sauce with cornstarch. The crowd thickened near the doorway.
To make or become more intense, intricate, or complex: The leader's departure thickens the problems. Our apprehension thickened.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.