Afloat

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Old English on flote (see a-2, float), influenced in Middle English by Old Norse á flot(i ) and Old French en flot .

wiktionary

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a- +‎  float

etymonline

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afloat (adv., adj.)

Old English aflote, contraction of prepositional phrase on flot; see a- (1) "to" + flot "body of water deep enough for a boat" (see float (n.)).