A lot vs. Alot: 9 Grammatical Pitfalls
late 13c. as a form of address, 1570s as a synonym for "loved one;" from sweet (adj.) + heart. As an adjective, with reference to labor contracts, it is attested from 1959.
Something that makes a deal more attractive; encouragement or enhancement, such as a monetary payment: sweetener was all I needed for the deal