Since this has been a hot subject of discussion in a current thread, it is well to bring it to the attention of all. It was Aristotle’s contention that , " Nature is the principle of motion and rest in those things which are such, per se. What he meant is that every substance which exists, which can be identified as a substance in its own right and not as an accident in some substance, has a nature which is an expression of its constituent principles of matter and form. And from this nature ( also called essence or substance flow all the physical elements of the substance as well as its natural and characteristic behaviors and powers.
Thus all living and non-living substances have a very specific nature which can be identified by the observation of those elements and behaviors and powers which are typical of a particular substance.
It is partially on this bases that the sciences typically categorize the substances it studies. But generally science does not call these substances natures. It typically gives them a name like iron, water, hydrogen, man, animal, cat, dog, etc. The name stands for a large group of individuals which can be grouped under this name. In other words, the name science gives stands for a type of nature which exists in numerous individuals. So the name or nature is used both universally and specifically as existing in individuals.
From the old Catholic Encyclopedia we have the following definition:
" In scholastic philosophy, nature, essence, and substance are closely related terms. Both essence and substance imply a static point of view and refer to constituents or mode of existence, while nature implies a dynamic point of view and refers to innate tendencies. Moreover, substance is opposed to accidents, whereas we may speak of the nature and essence not only of substances but also of accidents like colour, sound, intelligence, and of abstract ideals like virtue or duty. But when applied to the same substantial being, the terms substance, essence, and nature in reality stand only for different aspects of the same thing, and the distinction between them is a mental one. Substance connotes the thing as requiring no support, but as being itself the necessary support of accidents; essence properly denotes the intrinsic constitutive elements by which a thing is what it is and is distinguished from every other; nature denotes the substance or essence considered as the source of activities. "Nature properly speaking is the essence (or substance) of things which have in themselves as such a principle of activity (Aristotle, “Metaphysics”, 1015a, 13). By a process of abstraction the mind arises from individual and concrete natures to those of species and genera. "