be on one's back

noun

1. the part of the body opposite to the front; in humans and many other animals, the part to the rear or top reaching from the nape of the neck to the end of the spine
2. the backbone or spine
3. the part of a chair that supports one's back
4. the part of a garment or harness that fits on the back of a person or animal
5. physical strength: put some back into the work
6. the rear or hinder part of anything; part behind or opposite the front: the back of the room, the back of his leg
7. the part or side of anything that is less often used, seen, etc.: the back of the hand; the back of a carpet, textile, etc.; the back of a knife
8. 1. the part of a book where the sections are sewed or glued together; part covered by the spine
   2. the spine of a book
9. Mining the roof or overhead part of an underground passage
10. Sports a player positioned behind many of his or her teammates, as a running back in football or a halfback in soccer

adjective

1. at the rear or back; behind
2. distant or remote: back country
3. of or for a time in the past: a back copy of a newspaper, back pay
4. in a backward direction; returning; reversed: a back step
5. Phonet. articulated with the tongue toward the back of the mouth: said of certain vowels, as (o̵̅o̅) in cool

adverb

1. at, to, or toward the rear; backward
2. to or toward a former position or location
3. into or toward a previous condition
4. to or toward an earlier time
5. so as to keep in reserve or concealment: to hold back information
6. in return or requital: to pay someone back

transitive verb

1. to cause to move backward, or to the rear: often with up
2. to be at the back of; stand behind
3. to support or help, as with money, endorsement, etc.
4. to make a wager in support of; bet on
5. to get on the back of; mount
6. to provide with a back or backing
7. to form the back of
8. to sign on the back; endorse
9. to provide security for (a currency, loan, etc.)

intransitive verb

1. 1. to move or go backward: to back into a room
   2. to move (into a desired position) through the faulty performance of an opponent: to back into a championship
2. to have the back in a certain place or direction: the house backs on a lake
3. Meteorol. to shift counterclockwise (in the Northern Hemisphere): said of the changing direction of a wind