Joseph, your instructors were absolutely correct - in their profession the distinction is critical. For most people the "layman's" definitions as shown in the dictionary normally applies. A horticulturalists dictionary entry on soil would probably take up many pages. Every profession, art or specialty has it's own terminology, nomenclature and refinement of everyday language in order to communicate what is important to them. An example of this that one of my college classes used: In the English language we have one word for snow. The Eskimos have 20 (I don't recall the exact number).