what is the difference between literary devices and figures of speech

A figure of speech is the use of words to signify something other , than or beyond their literary meaning. For example: simile, metaphor. They are not literally true or correct, but amazes us with a comparison that is apt. for example: He is a lion in the field. ( He is not literally a lion, but displays the courage and qualities of a lion.)

A literary device is the clever use of words to create meaning, symbols, rhyme, rhythm. For example: alliteration, onomatopoeia, etc.