Definition of "bullish"

Sitting on the edge of the stage at the show’s end, draped in a flag and singing You Need Me, a bullish screw-you written when he was 15, he didn’t look much like a man still plagued by nerves over headlining Glastonbury.

2017 June 26, Alexis Petridis, “Glastonbury 2017 verdict: Radiohead, Foo Fighters, Lorde, Stormzy and more”, in the Guardian‎

It [the plan] was bullish about the prospects for BR winning new business and retaining what it had, but recognised that this would depend on the extent to which equipment would enable improved services at lower costs.

2023 March 8, David Clough, “The long road that led to Beeching”, in RAIL, number 978, pages 41–42