A person or thing providing supplementary or additional help and support. The hospital hired an auxiliary to assist with the increased number of patients.
A group or organization that provides supplementary support to a main group, often in a military or emergency context. The local fire department's auxiliary was called in to help during the large forest fire.
A vessel or vehicle used to provide additional support, often in a naval context. The navy deployed an auxiliary to supply the fleet with necessary provisions.
A verb that is used to form the tenses, moods, or voices of other verbs; an auxiliary verb. "Have" is the perfect-aspect auxiliary in "I have eaten."