indefinable
adjective uk/ˌɪn.dɪˈfaɪ.nə.bəl/ us/ˌɪn.dɪˈfaɪ.nə.bəl/ (also undefinable)
难下定义的;难以确切描述（或解释）的
impossible to clearly describe or explain
She had that indefinable something that went beyond mere sex appeal. 她具有某种说不清的气质，不只是性感。