Transition, n.
Etymology: [L. transitio: cf. F. transition. See Transient.]
1. Passage from one place or state to another; charge; as, the transition of the weather from hot to cold. There is no death, what seems so is transition. Longfellow.
2. (Mus.)
A direct or indirect passing from one key to another; a modulation.
3. (Rhet.)
4 more senses
A passing from one subject to another. [He] with transition sweet, new speech resumes. Milton.
4. (Biol.)
Change from one form to another.
Note: This word is sometimes pronounced tran*sish"un; but according to Walker, Smart, and most other authorities, the customary and preferable pronunciation is tran*sizh"un, although this latter mode violates analogy. Other authorities say tran*zish"un. Transition rocks (Geol.), a term formerly applied to the lowest uncrystalline stratified rocks (graywacke) supposed to contain no fossils, and so called because thought to have been formed when the earth was passing from an uninhabitable to a habitable state.
Shades of meaning
Fernald has no entry of its own for transition; he lists it under change, motion.
Where he writes about it:
Transition is change by passing from one place or state to another, especially in a natural, regular, or orderly way; as, the transition from spring to summer, or from youth to manhood. — from change
Motion is change of place or position in space; transition is a passing from one point or position in space to another. — from motion