An <u>adverb</u> is a word that is <u>modifying</u> a verb (or another adjective) and is formed through an <em>adjective</em> plus the <em>-ly</em> suffix.
The function of an <u>adverb</u> depends on a particular sentence, they can either determine the <u>degree</u>, frequency, or the time, describing <u>how</u> something is being done or at <u>what level</u>.
It emphasizes how severely the bubonic plague affected people and how quickly it killed them. ... It suggests that Europe could have easily avoided the plague if they had not let the ship in to the port.