adjective

Providing necessary support to the primary activities or operation of an organization, system, etc.

ancillary staff

ancillary,subordinate,secondary,supportive

noun

A person whose work provides necessary support to the primary activities of an organization, system, etc.

the employment of specialist teachers and ancillaries

replacement,deputy,relief,proxy,reserve,surrogate,cover,fill-in,stand-in,standby,locum,locum tenens,understudy,stopgap,alternative,ancillary