RhymeZone: topline definitions

Definitions of topline:

noun: The upper curvature of a horse's or dog's withers, back, and loin.
noun: Principal billing.
verb: (transitive) To bill (a performer) as the primary entertainer in a production.
verb: (transitive, intransitive) To be billed as the primary entertainer in (a production).

(Definitions from Wiktionary)