During the last couple of years we (an economist and an ecologist) have been doing joint research on multiple ecosystem services across countries and continents. Realizing that environmental scientists of different disciplines sometimes use the same words - such as sustainability or efficiency - with distinct meanings, a crucial basis for our successful teamwork has been to define clear terminology and a mutual understanding of what we are talking about. Our impression was that many scientists, practitioners, and politicians feel the same, and would appreciate greater clarity concerning technical terms sometimes used in a colloquial way. This situation motivated us to write this essay. The Millennium Ecosystem Assessment has shown that it is an ambitious task to combine fragmented and disciplinary knowledge in a common inter- and transdisciplinary language. Our essay is meant to take up part of this challenge.