| Iacchus | | | Gender: | Male | | Origin: | Latin |
| | | | | Latin form of Greek Iakchos, meaning "to shout". |
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| Iacobus | | | Gender: | Male | | Origin: | Latin |
| | | | | Latin form of Jacob, meaning "supplanter". |
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| Iacomus | | | Gender: | Male | | Origin: | Latin |
| | | | | Variant of Latin Iacobus, meaning "supplanter". |
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| Iagan | | | Gender: | Male | | Origin: | Scottish |
| | | | | Scottish variant of Aodhagan, meaning "fire". |
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| Iago | | | Gender: | Male | | Origin: | Welsh |
| | | | | Spanish and Welsh form of James, meaning "supplanter". |
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