It is a stop valve placed on an auxiliary piece of equipment. Or it could be placed at the steam main to feed an auxiliary steam system (heating, auxiliary pumping. etc.). It is not the Main steam stop for the boiler or the prime mover (engine, turbine, process), it is for a secondary service.

The auxiliary of the future verb of the verb "do" is "will".

Auxiliary sound refers to auxiliary interface connector where one can connect external sound devices.

What to do before starting auxiliary engine?

Polish Auxiliary Corps was created in 1916.