say it: uhn-bee-NOHNST
unbeknownst is an adjective and adverb meaning "(usually used with `to') occurring or existing without the knowledge of". It carries 2 recorded senses.
Definitions, synonyms and semantic relations for unbeknownst come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.