Inventing a Word for It

Pop quiz time!

The word “vellichor” is:

a. An adjective describing an agitated, violent state
b. A term taken from Latin meaning “one who sings”
c. The name of an alien species in the “Frigid Worlds” series of sci-fi novels
d. A word indicating the strange wistfulness of used bookstores

Ready? Have you chosen your final answer? No going back and switching to a different choice. No cheating either.