The Sindarin name for orc is orch, plural yrch. Boths meaning simply orc and orcs. But I guess you're looking for an older word only used in SILM: Glamhoth which means "noise-horde" or "noise-host" - The word is reflected in the name of Gandalfs sword: Glamdring: "Foe-hammer" / "Noise-horde-hammer" ... hope that is accurate enough for you
