box and cox
coalternate
intervolve
interden
interlace
one-on-one
interchange
double-handedly
pendant
two-handed
doublet
battle of the sexes
cross-handed
discord
alternize
disaccord
pair off
disagree
have a foot in both camps
co-
doubly
better
divide
six and two threes
vagrate
twosome
duet
duo
apart
pass
couple
in between
set up
dispair
multialternative
shuttle
as the case may be
chemistry
whatever the case may be
on the horns of a dilemma
to and fro
bothridial
differ
biune
codual
interoptode
surrogatum
tweely
opposite
split
ambidirectional
'tween
drive a wedge between
between
unwed
interdistinguish
bind
diarchy
duad
third-wheel
coexperience
wherebetween
interpermeate
betweenity
interpersonal chemistry
alchemy
dichotomize
go-together
set off
subrogate
varify
intermental
mixed
prelation
obverse
alternative
appose
two-time
incrustate
understanding
odd couple
selected
reverse
stand in for
discern
Tweedledee and Tweedledum
Tweedledum and Tweedledee
twinstick
wear two hats
tandemwise
coexchangeable
duopolistically
double
dualistically