Capitis deminutio or capitis diminutio (lit. "decrease of head") is a term used in Roman law, referring to the extinguishing, either in whole or in part, of a person's former legal capacity. As the Romans only used majuscule letters (capital) and had no minuscule letters, this does not refer to capital letters in a name.
There were three changes of state or condition attended with different consequences: maxima, media, and minima. The greatest, capitis deminutio maxima, involved the loss of liberty, citizenship, and family (e.g. being made a slave or prisoner of war). The next change of state, capitis deminutio media, consisted of a loss of citizenship and family without any forfeiture of personal liberty. The least change of state, capitis deminutio minima, consisted of a person ceasing to belong to a particular family, without loss of liberty or citizenship.
Blacks Law Dictionary provides the following definition:
Capitis Diminutio (meaning the diminishing of status) In Roman law. A diminishing or abridgment of personality; a loss or curtailment of a man's status or aggregate of legal attributes and qualifications.
Capitis Diminutio Minima (meaning a minimum loss of status) - The lowest or least comprehensive degree of loss of status. This occurred where a man's family relations alone were changed. It happened upon the arrogation [pride] of a person who had been his own master, (sui juris,) [of his own right, not under any legal disability] or upon the emancipation of one who had been under the patria potestas. [Parental authority] It left the rights of liberty and citizenship unaltered. See Inst. 1, 16, pr.; 1, 2, 3; Dig. 4, 5, 11; Mackeld. Rom.Law, 144.
Capitis Diminutio Media (meaning a medium loss of status) - A lessor or medium loss of status. This occurred where a man loses his rights of citizenship, but without losing his liberty. It carried away also the family rights.
Capitis Diminutio Maxima (meaning a maximum loss of status) - The highest or most comprehensive loss of status. This occurred when a man's condition was changed from one of freedom to one of bondage, when he became a slave. It swept away with it all rights of citizenship and all family rights.
Diminutio. Lat. In civil law. Diminution; a taking away; loss or depravation.
Capite. - Lat. By the head.