Decease, v. i. [imp. & p. p. Deceased; p. pr. & vb. n. Deceasing.]
To depart from this life; to die; to pass away. She's dead, deceased, she's dead. Shak. When our summers have deceased. Tennyson. Inasmuch as he carries the malignity and the lie with him, he so far deceases from nature. Emerson.
1 other Webster entry under this spelling
Decease, n.
Departure, especially departure from this life; death. His decease, which he should accomplish at Jerusalem. Luke ix. 31. And I, the whilst you mourn for his decease, Will with my mourning plaints your plaint increase. Spenser.
Syn. -- Death; departure; dissolution; demise; release. See Death.
Shades of meaning
Fernald has no entry of its own for decease; he lists it under die.
He lists it without comment; the entries above explain its neighbors.