late 14c., "death," a sense now obsolete, from Old French obit or directly from Medieval Latin obitus "death" (a figurative use, literally "a going down, a going to a place"), noun use of past participle of Latin obire "to die," literally "to go toward" (see obituary).
From c. 1400 as "anniversary of a person's death; memorial service held on the anniversary of a person's death." In modern usage (since 1874) it is usually a clipped form of obituary, though it had the same meaning of "published death notice" 15c.-17c. The scholarly abbreviation ob. with date is from Latin obiit "(he) died," third person singular of obire.