From Longman Dictionary of Contemporary Englishside orderˈside ˌorder noun [countable] DFa small amount of food ordered in a restaurant to be eaten with a main meal but served on a separate dish a side order of onion rings
Examples from the Corpus
side order• We had grilled chicken dark meat over rice with a little sauce, and a side order of steamed green beans.• The safest option is often a single, enormous sausage and a side order of disintegrating baked beans.• He also had a side order of Navy bean soup, a cottage-cheese salad and cherry pie.• This is chutzpah on rye bread with a side order of pickles and sour cream. 