Definition of back:
(v) :
(Not comparable) To a
previous condition or place; away from the front or from an edge
"he gave back the money."
(adj) :
near the
rear; in the previous state or position
"go in the back door of the house."
(n) :
the side of something opposite the
front or useful side; the
reverse side; the side that is not normally seen; that which is
farthest away from the front
"turn the book over and look at the back cover."