What is the simile used in the first verse of the poem "I Wandered Lonely as a Cloud" by William Wordsworth?

The simile of course is the the poet’s comparison of himself to a cloud. The simile has a double purpose: on the one hand, it assigns a human emotion (loneliness) to an inanimate object (the cloud), but on the other hand, it assigns the attributes of a cloud (floating, aimless, unconfined by earthly obstacles) to the poet’s activity (wandering). In this way poet and nature are combined poetically.

This is important when we consider the rest of the poem. The poet sees a “host of golden daffodils” “fluttering and dancing” beside a lake. The flowers, like the cloud, are assigned a human activity (dancing), as are the waves of the lake (“The waves beside them danced; but they / Out-did the sparkling waves in glee"). The entire scene – flowers, water, and the cloud/poet witnessing it -- is one of delight and harmony, inspiring a similar feeling in the poet (“A poet could not but be gay, / in such a jocund company”).

Wordsworth is not arguing that he “is” a cloud or that the flowers really are “dancing,” but the shift in tone (and scene) at the end of the poem – “when on my couch I lie / In vacant or in pensive mood” – underlines the importance of his vision nevertheless. It “flashes on his inward eye” – his imagination – and recalls him from his cares.