1In addition to one's regular job or as a subsidiary source of income.
- ‘no one lived in the property, but the caretaker made a little on the side by letting rooms out’
2Secretly, especially with regard to a relationship in addition to one's legal or regular partner.
covertly, without anyone knowing, in secret, in private, privately, in confidence, confidentially, behind closed doors, behind the scenes, behind someone's back, under cover, under the counter, discreetly, unobserved, quietly, furtively, stealthily, on the sly, on the quiet, privily, conspiratorially, clandestinely, on the side
- ‘Brian had a mistress on the side’
3North American Served separately from the main dish.
- ‘a club sandwich with French fries on the side’
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