whereupon

UK: /ˌ^hwɛərəˈpɒn/

US: /ˌhwɛrəˈpɑn, -ˈpɔn, ˌwɛr-; ˈhwɛrəˌpɑn, -ˌpɔn, ˈwɛr-/

US: (hwâr′ə pon′, -pôn′, wâr′-; hwâr′ə pon′, -pôn′, wâr′-)

WordReference Random House Learner's Dictionary of American English © 2026

where•up•on /ˌhwɛrəˈpɑn, -ˈpɔn, ˌwɛr-; ˈhwɛrəˌpɑn, -ˌpɔn, ˈwɛr-/   conj. 

1. upon what or which.
2. at or after which:
   He'll surely try to get in touch with her, whereupon we'll spring the trap.

WordReference Random House Unabridged Dictionary of American English © 2026

where•up•on  (hwâr′ə pon′, -pôn′, wâr′-; hwâr′ə pon′, -pôn′, wâr′-), conj. 

1. upon what or upon which.
2. at or after which.
3. [Archaic.] upon what?

• Middle English wherupon. See where, upon 1300–50

Collins Concise English Dictionary © HarperCollins Publishers::

whereupon / ˌwɛərəˈpɒn/ sentence_connector

1. at which; at which point; upon which