ar·son 
(ärsən)
(ärsən)n.
1. The crime of intentionally and illegally setting fire to a building or other structure.
2. An instance of this crime: a rash of arsons.
[Anglo-Norman, from Late Latin ārsiō, ārsiōn-, from Latin ārsus, past participle of ārdēre, to burn; see as- in the Appendix of Indo-European roots.]
arson·ist n.