účinný angolul

powerful▼(having or capable of exerting power, potency or influence)
adjective
[UK: ˈpaʊə.fəl] [US: ˈpaʊər.fəl]

efficient▼(using a particular proportion of available energy)
adjective
[UK: ɪ.ˈfɪʃnt] [US: ə.ˈfɪ.ʃənt]