These words are almost identical in meaning, and at first glance appear to have the same etymology; but according to OED, they came from two very different origins.
“Cogitation” comes from a Latin word which was a contraction of co- + the Latin for “agitate” (one of the senses of “agitate” being “to turn over in the mind, revolve, weigh, consider"), so co-agitare became cogitare.
“Cognition” is basically co- + the Greek for “know” (co-gnostic).
So we have an example of two different Latin words evolving toward eachother. Is this a coincidence? Could the contraction of the former occur as a result of influence from the latter? I don’t have dates for the earliest examples of these words, so I can’t verify anything. Anyone else?
Are there other examples like this that people can find?