Synonyms for Back up:

n.

capture, burn, fall back, archive, access, retrogress, retreat, block, browse, withdraw, call up, author, burn-in. sympathize, get behind, align, ally, help, promote, agree with, speak up for, stand by. validate, assert, make/prove your/a point, show, certify, vouch for, prove, point to. pardon me, HUH, again, What, come again, excuse me, I'm sorry, run that by me again, I beg your pardon. conduit, airlock, cutoff, cesspit, blockage, downspout, carry, culvert. pull away, back away, shrink, part, backtrack, stand aside, draw back, scatter. filter, bottleneck, jam, congestion, bumper-to-bumper, congestion charge, busy, gridlock. fail, break down, shut off, stop, go down, burn out, break, go off, cut out, run down. carve up, box in, buckle up, car pool, bus, change down, bypass, block in. back up (noun)
choke, back down, clog up, congest, choke off, back off, back, clog, support, foul.

v.

change (verb)
back.
move backward (verb)
fall back, withdraw, retreat.
social (verb)
support.
support (verb)
help, stand by, promote, back.

Other synonyms:

conduit, downspout, bumper-to-bumper, culvert, gridlock, blockage, congestion charge, cesspit, change down, author, box in, bottleneck, car pool, buckle up, call up. cutoff, congestion, burn-in, block in, block, airlock, jam. capture, busy, cut out, pull away, burn, archive, carve up. bus, stop, bypass, access. filter. carry. defend
speak up for, stand by.
Other relevant words:
prove, validate, certify, back away, withdraw, promote, backtrack, retrogress, help, retreat, show, fall back, vouch for, carry, get behind, back.