The Collaborative International Dictionary of English v.0.48:

Obit \O"bit\, n. [OF. obit, L. obitus, fr. obire to go against,
   to go to meet, (sc. mortem) to die; ob (see Ob-) + ire to go.
   See Issue.]
   1. Death; decease; the date of one's death. --Wood.
      [1913 Webster]

   2. A funeral solemnity or office; obsequies.
      [1913 Webster]

   3. A service for the soul of a deceased person on the
      anniversary of the day of his death.
      [1913 Webster]

            The emoluments and advantages from oblations, obits,
            and other sources, increased in value. --Milman.
      [1913 Webster]

   4. Same as obituary; -- by shortenting.
      [PJC]

   Post obit [L. post obitum]. See Post-obit.
      [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

POST OBIT, contract. An agreement, by which the obligor borrows a certain
sum of money and promises to pay a larger sum, exceeding the lawful rate of
interest, upon the death of a person, from whom he has some expectation, if
the obligor be then living. 7 Mass. R. 119; 6 Madd. R. 111; 5 Ves. 57; 19
Ves. 628.
     2. Equity will, in general, relieve a party from these unequal
contracts, as they are fraudulent on the ancestor. See 1 Story, Eq. Sec.
842; 2 P. Wms. 182; 2 Sim. R. 183, 192; 5 Sim. R. 524. But relief will be
granted only on equitable terms, for he who seeks equity must do equity. 1
Fonb. B. 1, c. 2, Sec. 13, note, p; 1 Story, Eq. Sec. 344. See Catching
Bargain; Macedonian Decree.