What is the X in X-mas?
1510s, from Middle French elegie, from Latin elegia, from Greek elegeia ode "an elegaic song," from elegeia, fem. of elegeios "elegaic," from elegos "poem or song of lament," perhaps from a Phrygian word.
A form of poetry that mourns the loss of someone who has died or something that has deteriorated. A notable example is the “Elegy Written in a Country Churchyard,” by Thomas Gray. (Compare eulogy.)