What is the X in X-mas?
early 15c., from Latin salubritas, from salubris "promoting health, healthful" (see salubrious).
1540s, from Latin salubris "promoting health, healthful," from salus (genitive salutis) "welfare, health" (see salute (v.)). Related: Salubriously; salubriousness.
salubrious sa·lu·bri·ous (sə-lōō'brē-əs)adj. Conducive or favorable to health or well-being.