n. A genus of xylophagous coleopterous insects, giving name to a family Cioidæ or Cisidæ.n. A prefix of Latin origin, signifying ‘on this side of,’ forming adjectives with names of rivers, mountains, etc.n. An abbreviation (in cis θ) for (cos θ + i sin θ): in function theory: as, x = ξ + i η = ρ (cos θ + i sin θ) = ρ cis θ.