What is the X in X-mas?
late 14c., from Old French transgression (12c.), from Late Latin transgressionem (nominative transgressio) "a transgression of the law," in classical Latin, "a going over," from transgressus, past participle of transgredi "go beyond," from trans- "across" (see trans-) + gradi (past participle gressus) "to walk, go" (see grade).
A relative rise in sea level resulting in deposition of marine strata over terrestrial strata. The sequence of sedimentary strata formed by transgressions and regressions provides information about the changes in sea level during a particular geologic time. Compare regression.