‘Function’ is a key concept in both evolutionary biology and bioinspired design. Distilling a problem to essential functions allows designers to look to evolved traits that perform analogous functions in biological systems. However, ‘function’ has a fraught philosophical history in evolutionary biology because it often assigns purpose to a trait that goes beyond the evolutionary processes that led to the origin of that trait. Here we review three key sets of ideas from evolutionary and organismal biology that can broaden and clarify biomimetic approaches by more explicitly and carefully considering ‘function.’ First, mapping a trait of interest within the integrated fitness of an organism can clarify limits to copying a particular adaptation for a human application. Second, detailing the dependency of a trait on other traits, and levels, within an organism can clarify the extent to which a designer must replicate other organismal traits for a given function. Third, some traits may show a derived function as a byproduct of selection (e.g., a spandral), and considering functional byproducts gives clues for where to search for inspiration in human bio-inspired design. We develop a conceptual framework that draws from key concepts in evolutionary and organismal biology to aid engineers and designers in their search for biological inspiration.