the natural coloring of tissues, surfaces, or structures; contributing to the characteristic hues or tones observed in animals, plants, or human beings
the study of the behavior of air as it interacts with solid objects, particularly the flow of air around and through objects, and the effects of this interaction on the objects
each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, leading to variation in atomic mass