From the given options, select the Figure of Speech (Poetic Device) used in the expression:

As tough as leather

Simile

The figure of speech used in the expression "As tough as leather" is simile.

A simile is a figure of speech in which two things are compared using the words "like" or "as." In this case, the toughness of something is being compared to the toughness of leather. This creates a sense of the thing's durability and strength.

The other answer choices are incorrect. Pun is a play on words. Oxymoron is a figure of speech in which two contradictory terms are used together. Alliteration is the repetition of consonant sounds at the beginning of words. None of these devices are used in the expression "As tough as leather.".