Where does “penumbra” come from?

penumbra (Latin) comes from Latin umbra, from Old Latin omra, from Proto-Indo-European h₂mr-u-.

Ancestry of “penumbra”, step by step

penumbra traces back through two separate lines of ancestry.

via Latin umbra

StepLanguageWordMeaning
1Latinumbraa shadow; a shade; a ghost
2Old Latinomra—
3Proto-Indo-Europeanh₂mr-u-—

via Latin paene

StepLanguageWordMeaning
1Latinpaenealmost, nearly; scarcely, hardly, barely
2Proto-Indo-Europeanpeh₁-to hate, hurt
Every word from Proto-Indo-European h₂mr-u- →Every word from Old Latin omra →Every word from Latin umbra →