Plural of ancillary; things that are subordinate, supportive, or of secondary importance.
From Late Latin 'ancillaris' (adjective meaning of or relating to a maidservant), which English adapted as 'ancillary,' then added the plural '-ies'.
In modern business, 'ancillary services' (like baggage fees) are profits hidden in plain sight—companies learned that what seems subordinate can be where the real money lives.
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