1.the rear surface of the human body from the shoulders to the hips.

“he lay on his back”
the upper surface of an animal’s body that corresponds to a person’s back.
“the adults have white bodies with grey backs”
the spine of a person or animal.
synonyms: spine, backbone, spinal column, vertebral column; More
the main structure of a ship’s hull or an aircraft’s fuselage.
“Demetrius broke its back on the rocks in a force 11 gale”
the part of a garment that covers a person’s back.
“a top with a scooped neckline and a low back”
a person’s back regarded as carrying a load or bearing an imposition.
“the Press are on my back”

2.the side or part of something that is away from the spectator or from the direction in which it moves or faces; the rear.

“at the back of the hotel is a secluded garden”
synonyms: rear, rear side, other side; More
antonyms: front, head
the position directly behind someone or something.
“she unbuttoned her dress from the back”
the side or part of an object that is not normally seen or used.
“the back of a postcard”
synonyms: reverse, reverse side, other side, underside; More
antonyms: front, face
the part of a chair against which the sitter’s back rests.

3.a player in a team game who plays in a defensive position behind the forwards.

“their backs showed some impressive running and passing”

4.the grounds of Cambridge colleges which back on to the River Cam.

1.in the opposite direction from the one that one is facing or travelling towards.
“he moved back a pace”
synonyms: backwards, behind one, to one’s rear, rearwards; More
antonyms: forward
expressing movement of the body into a reclining position.
“he leaned back in his chair”
at a distance away.
“keep back from the roadside”
synonyms: away, at a distance
“keep back from the roadside”

NORTH AMERICAN informal
behind.
“he knew that other people were back of him”
NORTH AMERICAN informal
losing by a specified margin.
“the team was five points back”
2.so as to return to an earlier or normal position or condition.
“she put the book back on the shelf”
at a place previously left or mentioned.
“the folks back home are counting on him”
fashionable again.
“sideburns are back”
3.in or into the past.
“he made his fortune back in 1955”
4.in return.
“they wrote back to me”

1.give financial, material, or moral support to.

1.of or at the back of something.
“the back garden”
synonyms: rear More
antonyms: front
in a remote or subsidiary position.
“back roads”
2.from or relating to the past.
“she was owed back pay”
synonyms: past, old, previous, earlier, former, out of date
“back copies of the journal”
antonyms: future
3.directed towards the rear or in a reversed course.
“a back header”
4.PHONETICS
(of a sound) articulated at the back of the mouth.
“a long back vowel, as in ‘dance’ or ‘bath'”