Recent scholarship posits that ambiguous (‘polysemic’) ideas are effective for coalition building between diverse stakeholders: their capacity to be interpreted differently attracts different interests. Hence, in search of political solutions to ‘wicked’ and similarly complex problems, deploying polysemic ideas would be critical to effective policy-making. This paper scopes the policy-making potential of polysemic ideas by examining the impact of an ambiguous concept known as ‘One Health’ on responses to antimicrobial resistance (AMR) in Australia and the UK. It offers two primary arguments. Firstly, polysemic ideas can help mobilise broad attention to complex problems: since One Health became associated with AMR, political and administrative attention has grown more intense and coordinated than previously. Secondly, however, a polysemic idea alone may be insufficient to generate effective action: the contrast between Australian and UK AMR policies illustrates that polysemic ideas do not suspend interests, institutions, or ideas that can be readily deployed.