The sentence 'I wandered lonely as a cloud' is a-

Simile:

দুটি ভিন্নধর্মী জিনিসের মধ্যে As বা like দ্বারা তুলনা বোঝালে তাকে Simile বলে। (The comparison of unlike things using the words like or as is known to be simile)

i) My heart is like a singing bird
ii) He is as cunning as a fox.
iii) I wandered lonely as a cloud.
iv) The soul was like a star dwelt apart
v) Our soldiers are as brave as lions.