¹ back noun

• the rear part of the body : the part of the body that is opposite to the stomach and chest and that goes from the neck to the top of the legs
• the part of an animal that is like a person's back
• the side or surface of something that is opposite the front or face : the rear side or surface of something—usually singular

² back adverb

• in, toward, or at the back or rear
• to, toward, or in the place where someone or something was previously
• in or into the past : backward in time; also : ago

³ back adjective

• of or relating to the back : located at the back
• far from a central or main area
• not yet paid : owed from an earlier time

⁴ back verb

• to give help to (someone) : support
• to bet on (someone or something)
• to provide evidence that supports (something)