What is the X in X-mas?
"encysted tumor," 1706, medical Latin, from Greek atheroma, from athere "groats, porridge" (related to ather "chaff"), in reference to what is inside. For ending, see -oma.
atheroma ath·er·o·ma (āth'ə-rō'mə)n. pl. ath·er·o·mas or ath·er·o·ma·ta (-mə-tə) A deposit or degenerative accumulation of lipid-containing plaques on the innermost layer of the wall of an artery.