about-face
about-turn
accompaniment
advocate
agent
alter ego
alternate
alternative
amicus curiae
analogy
attorney
back track
back trail
backing
backing off
backing out
backing up
backup man
champion
change
changeling
comparison
copy
counterfeit
deputy
double
dummy
equal
equivalent
ersatz
exchange
executive officer
exponent
fake
figurehead
fill-in
ghost
ghostwriter
imitation
lieutenant
locum
locum tenens
makeshift
metaphor
metonymy
mock
next best thing
paranymph
personnel
phony
accretion
accumulation
approval
approving
blessing
duplicate
duplication
access
additional
audio
backups
built-in
default
digital
emergency
encryption
hardware
installation
monitor
recovery
storage
surveillance
tactical
update