Final answer:
In Chaucer's 'The Pardoner's Prologue,' line 55 uses the definition of 'vicious' as 'having the nature or quality of vice, immoral.'
Step-by-step explanation:
In Chaucer's usage of the word 'vicious' in line 55 of 'The Pardoner's Prologue,' it corresponds with definition 1: having the nature or quality of vice, immoral. The line suggests that the speaker is admitting to being a morally corrupt person, but still capable of telling moral tales. Thus, the usage of 'vicious' here aligns with the meaning of 'immoral.'