Dear SPOGG:Oh, how glad we are you asked this question. It gives us reason to revel in the glory that is the Oxford English Dictionary. Back in the day, we wished we had the money and space to accommodate the entire collection on our bookshelves. Now, this miracle can be searched online.
Has transition always been a noun AND a verb? I seem to remember reading/writing about someone 'making a transition,' but how about "She transitioned to her new job..." or "As we transition..." Is that correct, or is it 'new use' from today's 'new speak?'
But to the answer, anon!
Transition has been a noun since at least 1551, the first time it appeared in print. Its adventures as a verb have been more recent. The OED notes it first appeared thus in 1975, meaning it is too young to have ever seen an episode of The Partridge Family outside of reruns.
Here, by the way, is the online OED. Your library might subscribe. Be sure to check out the database and subscription services you can access with your library card.