| 1 | English | virulent | Of animals, plants, or substances: extremely... |
| 2 | French | virulent | virulent |
| 3 | Latin | virulentus | poisonous |
| 4 | Latin | -ulentus | adjective-forming suffix meaning abounding in,... |
| 5 | Latin | -entus | adjective-forming suffix meaning abounding in,... |
| 6 | Latin | cruentus | bloody in its various senses, "particularly:" |
| 7 | Latin | cruor | blood, gore; murder, bloodshed |
| 8 | Proto-Indo-European | krewh₂- | blood outside the body |