What is what part of speech is with?

The word "with" can function as several parts of speech, most commonly a preposition.

As a preposition, "with" indicates a relationship between a noun or pronoun and other words in the sentence. It expresses concepts like:

• Accompaniment or association: I went to the store with my friend.
• Possession or having: She's a girl with blue eyes.
• Means or instrument: He opened the door with a key.
• Manner or quality: She sang with enthusiasm.