Whereas

google

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late Middle English: from where + as1.

wiktionary

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From where +‎ as(“that”); first attested in the meaning of "where" [14thc.] [1]. Compare thereas.

etymonline

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whereas (adv.)

mid-14c., "where;" early 15c. as a conjunction, "in consideration of the fact that, considering that things are so; while on the contrary," from where (in the sense of "in which position or circumstances") + as.