the rear part of the human body, esp from the neck to the end of the spine

the corresponding part of a quadruped or other animal

the spine

the main structure of a ship or aircraft

the side or surface behind the front or face, e.g. the rear part or the farther or reverse side

something at or on the back for support

the final section of a book

the edge of a book along which the sections or pages are secured or glued

to, towards, or at the rear

She tied her hair back

in or into a reclining position

She told me to lie back

away, e.g. from the speaker

Stand back and give him air

in or into the past; ago

It happened three years back

nearer the beginning

Go back a couple of pages and read what it says there

to, towards, or in a place from which somebody or something came

He put it back on the shelf

to or towards a former state

He was asked to think back to his childhood

in return or reply

Ring me back

at or in the back

the back door

distant from a central or main area; remote

back roads

to support (somebody or something) by giving material or moral assistance

to give financial support to (a scheme or undertaking)

to provide (something, e.g. a chair) with a back

to be at or form the back of (something)