Final answer:
Juliet uses a metaphor in line 198 to describe her love, comparing it to a red, red rose.
Step-by-step explanation:
The literary device used by Juliet in line 198 is metaphor.
In this line, Juliet says, 'My love is like a red, red rose.'
By comparing her love to a rose, Juliet is conveying the beauty, fragility, and passion of her emotions.
This metaphor helps the reader understand Juliet's intense feelings for Romeo.