'Ten thousand saw I at a glance' is a figure of speech known as-

- Hyperbole is an exaggerated statement or an extreme overstatement.
- 'Ten thousand saw I at a glance' is a figure of speech known as Hyperbole. (Taken from the poem 'The Daffodils' by William Wordsworth).
Source: An ABC of English Literature, Dr. M Mofizar Rahman.