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Definitions

onset

[on-set, awn-] / ˈɒnˌsɛt, ˈɔn- /
NOUN
beginning; attack
Synonyms
STRONGEST
commencement dawning onslaught outbreak outset
STRONG
access aggression assault birth charge dawn encounter inception incipience kickoff offense offensive onrush opening origin rush seizure start
WEAK
assailment onfall outstart
Antonyms
STRONGEST
conclusion end
STRONG
completion death ending finish retreat

From Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.