Standby, reserve or extra.
Supporting, reinforcing; (music) of or related to accompaniment
That is intended as a backup.
reinforcements
A copy of a file or record, stored separately from the original, that can be used to recover the original if it is destroyed or damaged.
A reserve or substitute.
An accumulation of material caused by a (partial) obstruction or (complete) blockage of the flow or movement of the material, or an accumulation of material that causes an overflow due to the flow being greater than the maximum possible flow.
Placed in a lower class, rank, or position.
Descending in a regular series.
dependent on and either modifying or complementing the main clause
Submissive or inferior to, or controlled by authority.
To make subservient.
To treat as of less value or importance.
To make of lower priority in order of payment in bankruptcy.
One who is subordinate.