Definition of cowboy up in US English:

cowboy up

phrasal verb

US
informal
  • Make a determined effort to overcome a formidable obstacle.

    ‘Millar cowboyed up, but couldn't he have flipped the Enrique grounder to Pedro?’
    • ‘The detective cowboys up to hunt down the mysterious marauder.’
    • ‘But a man, she thought, was supposed to endure pain, cowboy up, and not bitch about it all day long.’
    • ‘Even the Texans were able to cowboy up in holding the Dolphins' defense without a sack.’
    • ‘Both sides need to cowboy up.’
    • ‘This would be an open attempt to get them to thinking that they need to cowboy up and put me in my place.’