Throw in Definition 1 of 4Pro Tip 1/3Unplanned Extra Indicates a bonus item or service given unexpectedly in addition to what's purchased. They threw in a phone case with my new smartphone. Pro Tip 2/3Negotiation Tool Used as a persuasive offer during negotiations to sweeten a deal. If you buy today, we can throw in an extended warranty. Pro Tip 3/3Not Always Literal The added item isn't always physical; it could be an additional service or favour. With every haircut, we throw in a complimentary scalp massage.