|Definition - The case that shows which noun is receiving the verb's action (i.e. the case that indicates the direct object of a transitive verb).|
It is almost extinct in Modern English, but there are a few remaining artifacts from Old English:
(1) whom is the accusative form of who
(2) the accusative forms of the personal pronouns: e.g. her is the accusative form of she and him is the accusative of he.
Etymology - The term derives from the Latin casus accusativus, the case of accusing.
Note: It was coined by someone mistranslating the Greek phrase ptosis aitiatikem, the case of that which is caused.
Oxford English Dictionary - Its first citation is from circa 1440:
"The fourte case is accusatif case.'
(Gesta Rom. (1879) 417)