A variant or misspelling of 'auxiliary'; serving in a supplementary or supporting role.
From Latin 'auxilium' (aid) + '-ary' (relating to). The form 'auxillary' with double-l appears to be a common misspelling of 'auxiliary,' possibly influenced by pronunciation patterns.
Auxillary is so frequently misspelled that some people wonder if it's an accepted variant—it's not, but the double-l spelling reveals how spelling competition still happens in English despite standardization efforts.
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