Cyaarside, also called cyarside, is the As≡C− anion.

Featuring a triple bond between arsenic and carbon, it is the arsenic analogue of cyanide and cyaphide.

An actinide cyaarside complex can be prepared by C−O bond cleavage of the arsaethynolate anion, the arsenic analogue of cyanate and phosphaethynolate.

[2] Reaction of the uranium complex [((Ad,MeArO)3N)UIII(DME)] with one molar equivalent of [Na(OCAs)(dioxane)2.5] in the presence of 2.2.2-cryptand results in the formation of a dinuclear, oxo-bridged uranium complex featuring a C≡As ligand.