astrophysicist (n.)

"a student of physics," 1836, from physics + -ist. Coined by the Rev. William Whewell, English polymath, to denote a "cultivator of physics" as opposed to a physician.

As we cannot use physician for a cultivator of physics, I have called him a physicist. We need very much a name to describe a cultivator of science in general. I should incline to call him a Scientist. Thus we might say, that as an Artist is a Musician, Painter, or Poet, a Scientist is a Mathematician, Physicist, or Naturalist. [William Whewell, "The Philosophy of the Inductive Sciences," London, 1840]

It was used earlier in the sense of "one versed in the medical sciences" (1716) but this was rare and by 19c. was obsolete.