Honestly

google

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Middle English (originally in the sense ‘held in or deserving of honour’): via Old French from Latin honestus, from honos (see honour).

wiktionary

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From Middle English honestly, honestlyche, honestliche, equivalent to honest +‎ -ly.

etymonline

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honestly (adv.)

mid-14c., from honest + -ly (2). As an intensifier or exclamation, from 1898.