Janus
ambiguity
ambivalence
bifidity
biformity
bifurcation
bipartition
bisection
branching
by two
conjugation
cutting in two
dichotomy
dimidiation
division
doubleness
doublethink
doubling
dualism
duality
duplexity
duplication
duplicity
equivocality
forking
in half
irony
pairing
polarity
ramification
subdivision
twinning
two-facedness
twoness
calving
having