This is not a literary term, but it confused more than one student. So, I am including it here.
coin (intransitive verb) means "to invent."
Thus, to "coin a verb" is to "invent a verb."
Shakespeare "coined" more than 1,700 words by changing nouns to verbs, making verbs adjectives, making new combination of words paired together, etc.
Example: Olivia: "There lies your way, due west."
Viola: "Then westward ho!"
From Shakespeare's Twelfth Night, Act III, Scene I, Line 135.
Some words Shakespeare coined: advertising, alligator, anchovy, countless, gust, investment, obscene, puke, puppy dog, tranquil, zany.