Which figure of speech is used in this text?
In the overmastering loneliness of that moment, his whole life seemed to him nothing but vanity.
—Robert Penn Warren, Night Rider

 - assonance
 - antithesis
The text uses assonance, the repetition of a vowel sound in a series of nearby words.
The words overmastering, loneliness, moment, and whole share a vowel sound.