1. Lacking in cunning, guile, or worldliness; innocent or naive: I'm not so ingenuous as to believe everything he says. See Synonyms at naive.
2. Straightforward or frank; candid: "I must be so ingenuous as to own that the accounts are not so certain as to the exact time and place of his birth" (Memoir of Martinus Scriblerus).
[Latin ingenuus, honest, freeborn; see genə- in the Appendix of Indo-European roots.]
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