defensible
adjective uk/dɪˈfen.sə.bəl/ us/dɪˈfen.sə.bəl/ (US also defendable)
有防卫能力的;合乎情理的，有正当理由的
able to be protected from attack, or able to be supported by argument
A city built on an island is easily defensible. 建在岛上的城市容易防守。
High petrol taxes are defensible on ecological grounds. 从保护生态环境的角度来讲，征收高额汽油税是有道理的。