[v] establish as valid or genuine; "Can you back up your claims?"
[v] become or cause to become obstructed; "The leaves clog our drains in the Fall"; "The water pipe is backed up"
[v] make a copy of (a computer file) esp. for storage in another place as a security cop; "You'd better back up these files!"
[v] move backwards from a certain position; "The bully had to back down"
[v] give moral or psychological support, aid, or courage to; "She supported him during the illness"