Yours, Etc.: Origins and Uses of 8 Sign-Offs
1610s, from French incapacité (16c.), from Medieval Latin incapacitatem (nominative incapacitas), from Late Latin incapax (genitive incapacis) "incapable," from in- "not" (see in- (1)) + Latin capax "capable," literally "able to hold much," from capere "to take" (see capable). Often used 17c. as a legal term referring to inability to take, receive, or deal with in some way.