What is the X in X-mas?
late Old English offrung "the presenting of something to a deity; a thing so presented," verbal noun from offrian (see offer (v.)). Of presentations to a person from mid-15c.; to the public from 1834.
Old English ofrian "to offer, show, exhibit, sacrifice, bring an oblation," from Latin offerre "to present, bestow, bring before" (in Late Latin "to present in worship"), from ob "to" (see ob-) + ferre "to bring, to carry" (see infer). The Latin word was borrowed elsewhere in Germanic, e.g. Old Frisian offria, Middle Dutch offeren, Old Norse offra. Non-religious sense reinforced by Old French offrir "to offer," from Latin offerre. Related: Offered; offering.
an oblation, dedicated to God. Thus Cain consecrated to God of the first-fruits of the earth, and Abel of the firstlings of the flock (Gen. 4:3, 4). Under the Levitical system different kinds of offerings are specified, and laws laid down as to their presentation. These are described under their distinctive names.