throw something in

Từ điển tiếng Anh - Cambridge Advanced Learners Dictionary

throw sth in phrasal verb before or after object [ threw sth in thrown sth in thrown sth in throws sth in throwing sth in ]
If a person or business selling goods throws something in, they provide it for free when you buy something else from them
• When I bought my new glasses, they threw in a free pair of prescription sunglasses.
Thesaurus⁺: ↑Including and containing ↑Comprising and consisting of
Main entry: throw_{phrasal verb}