postnasal drip

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The chronic secretion of mucus from the posterior nasal cavities, often caused by a cold or allergy.

Wiktionary

1. n. alternative spelling of post-nasal drip.

WordNet 3.0

1. n. chronic secretion of mucus from the rear of the nasal cavity into the nasopharynx