The development of terminology features heavily in language planning, and here the differences between planned and ethnic languages are much less pronounced. This is especially the case in languages with smaller numbers of speakers, or in indigenous and endangered languages such as Te Reo Māori of Aotearoa New Zealand that rely on language planning for their survival, and where conscious terminology planning is therefore commonplace. The present article compares the terminological principles that are applied in the creation of new terms in Te Reo Māori and the planned language Esperanto. Different preferences for endogenous versus exogenous ways of developing new words generate conflict in both language communities as they adapt to the demands of functioning in modern and international arenas. Long-term success in terminological planning can only be achieved by more comprehensive application of principles from terminological science to maximize the adequacy of the generated terms and their acceptance within the speech communities.