Maybe

google

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late Middle English: from the phrase it may be (that) .

wiktionary

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From an ellipsis of it may be, equivalent to may +‎ be. Compare mayhap.

etymonline

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maybe (adv.)

"perhaps, possibly," early 15c., from (it) may be; see may (v.1) + be (v.). In early 19c. still sometimes written as two words. As a noun, "something that may be or happen," 1580s.