In a class of its own; one of a kind. / (rarer) By itself; of its own.

(proscribed) A thing apart, an isolated specimen.

(law) A canon of construction holding that when a general term follows a list of particular terms, the general term only applies to things similar to the particular terms. For example, in the list "sun, moon, and other large objects", the phrase "other large objects" only includes celestial bodies, not houses and elephants.

Hatred for the human race.

(international law) A person who has committed a criminal act so grave – originally maritime piracy and slave-trading, and now torture as well – that any nation may put on trial and, upon conviction, punish him or her.

plural of hostis humani generis.