Lord that he is and my piety beyond reproach, here I am, my programming having taken a turn for the elemental and put me to thinking about twos. As an important concept in programming as symmetry a concept in art, other disciplines also keep the medial plane at their core, including language. As I have learned, the prefixes, roots, and combining forms expressing the number two outnumber the others by an impressive sum, and also outflank them in range of expression and conceptual domain.

Michael J. Sheehan, in his “Word Parts Dictionary”, provides the most comprehensive list I’ve found, and I reproduce it here.

Word Parts Expressing “Two”

• ambi- (both)

ambidextrous: using both hands with equal facility
ambisinister: clumsy or unskillful with both hands
ambivert: personality type exhibiting both extroversion and introversion

• ambo- (both)

amboceptor: a substance that, added to another, breaks down red blood cells
ambosexous: of both sexes; hermaphrodite

• amphi- (on both sides)

amphiboly: ambiguity of speech arising from uncertain grammar
amphioxus: sharp at both ends
amphivorous: eating both animal and vegetable food

• ampho- (on both sides)

amphogenic: producing both male and female offspring
amphora: large two-handled storage jar
amphoteric: capable of functioning either as an acid or as a base

• bi- (two)

bicipital: having two heads
bifurcate: to divide or fork into two branches
bimester: a two-month period

• bin- (two)

binary: consisting of, indicating, or involving two
binate: produced or borne in pairs
binaural: having two ears

• bis- (two; twice)

bismarine: between or washed by two seas
bissextile: extra leap year day in the Julian calendar

• deutero- (second)

deuterogamy: a second marriage
Deuteronomy: 5th book of the Pentateuch, with 2nd statement of Mosaic law
deuteropathy: any abnormality secondary to another pathological condition

• deuto- (second)

deutoplasm: reserve nutritive material in the ovarian cytoplasm
deutoscolex: a secondary scolex (headlike segment of a tapeworm)
deutotergite: the second dorsal segment of the abdomen of insects

• di- (two)

dicrotic: double beat of the pulse for each beat of the heart
diplegia: paralysis of the identical part on both sides of the body
dipterous: having two winglike appendages

• dicho- (in two)

dichogamous: having male and female elements at different times
dichotic: affecting the two ears differently
dichotomous: divided or dividing into two parts

• diphy- (double)

diphycercal: having the tail divided into two equal halves
diphyletic: derived from two lines of evolutionary descent
diphyodont: developing both temporary and permanent teeth

• diplo- (two; double)

diploblastic: having two germ layers, as the embryos of sponges
diploneurous: having two nervous systems
diplopia: double vision

• disso- (double)

dissogeny: in ctenophores, two periods of sexual maturity
dissology: repetition

• double- (in combination)

double-barreled: gun having two barrels, side by side or over and under
doubleheader: two events held consecutively on the same program
double-team: to guard an opponent with two players at one time

• du- (two)

duplation: multiplication by two
duplex: having two principal elements or parts
duplicate: existing in two corresponding or identical parts

• duo- (two)

duologue: a dialogue between two persons
duopoly: an oligopoly limited to two sellers
duopsony: market condition with only two buyers

• duplicato- (doubly)

duplicato-dentate: toothed leaves in which the teeth are also dentate
duplicato-serrate: serrated leaves whose notches are themselves serrate
duplicato-ternate: leaves themselves composed of three leaves each

• duplici- (duplex)

duplicidentate: rodents having two pairs of upper incisor teeth
duplicipennate: having two wings folded longitudinally in repose

• dyo- (two)

Dyophysite: person who says that Christ has both divine and human natures
Dyothelite: person who holds that Christ has both divine and human wills

• gemelli- (twin)

gemelled: coupled; paired
gemelliparous: producing twins
gemellous: duplicated

• gemin- (double)

gemination: doubling; duplication; repetition
geminiflorous: having flowers arranged in pairs
geminous: occurring in pairs

• twi- (double)

twibill: an adz/ax combination
twi-headed: two-headed
twi-night: baseball doubleheader in which the second game ends at night

• zyga-/zygo- (pair)

zygapophysis: paired processes of the neural arch of a vertebra
zygodactyl: having the toes arranged two in front and two in back
zygomorphic: having bilateral symmetry