agelast
One who never laughs (especially at jokes); a mirthless person.
rare
As a real agelast in a comedy, he is beaten. The beating of an agelast is the most important point of the comedy.
Where it comes from
Learned borrowing from Ancient Greek ἀγέλαστος (agélastos, “not laughing”), from γελάω (geláō, “to laugh”). Attributed to a French coinage by François Rabelais (ca.1483–1494—1553).
Adapted from the Wiktionary entry agelast (CC BY-SA 4.0).