I answer that, The effects of the soul's passions are sometimes named metaphorically, from a likeness to sensible bodies: for the reason that the movements of the animal appetite are like the inclinations of the natural appetite.
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic likeness passion
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“But that which is depressed is not consumed; nay, it is weighed down by something heavy, whereas that which is consumed enters within the consumer. Therefore depression should not be reckoned an effect of sorrow.
On the contrary, Gregory of Nyssa [*Nemesius, De Nat. Hom. xix.] and Damascene (De Fide Orth. ii, 14) speak of "depressing sorrow."
I answer that, The effects of the soul's passions are sometimes named metaphorically, from a likeness to sensible bodies: for the reason that the movements of the animal appetite are like the inclinations of the natural appetite. And in this way fervor is ascribed to love, expansion to pleasure, and depression to sorrow. For a man is said to be depressed, through being hindered in his own movement by some weight. Now it is evident from what has been said above (Q. 23, A. 4; Q. 25, A. 4; Q. 36, A. 1) that sorrow is caused by a present evil: and this evil, from the very fact that it is repugnant to the movement of the will, depresses the soul, inasmuch as it hinders it from enjoying that which it wishes to enjoy.” source