əˈmōnēəm, -nyəm noun
( -s )
Etymology: New Latin, from ammonia + -ium
: an ion NH 4 + or radical NH 4 derived from ammonia by combination with a hydrogen ion or atom and known in compounds (as salts formed by reaction of dry or aqueous ammonia with acids) that resemble in properties the compounds of the alkali metals and known also in organic compounds (as quaternary ammonium compounds) in which one or more of the hydrogen atoms attached to the nitrogen are substituted by organic radicals