There are a lot of words to represent two in English. Here I will not list pair, double, couple, or twin since these are too often used and are well known. Other languages also have more than one word for two, but probably not as many as those in English.
Although biped, doublet, or dyad is not commonly used, at least half of these variants regularly show up in reading material.
biped: an animal that uses two legs for walking.
deuce: (North American) the two on dice or playing cards. This word is also used in tennis matches.
doublet: something consisting of two identical or similar parts. The word is also used in poetry.
duet: a performance by two people, especially singers, instrumentalists, or dancers.
duplicity: deceitfulness; double-dealing.
dyad: something that consists of two elements or parts. It is used in math and chemistry.
tandem: a bicycle with seats and pedals for two riders, one behind the other. I actually saw this kind of bicycle once and was really surprised such things exist.
twosome: a pair of people considered together. It often used in dance.
couplet: two lines of verse, usually in the same meter and joined by rhyme, that form a unit.
duo: a pair of people or things, especially in music or entertainment. For example, a comedy duo.
duality: an instance of opposition or contrast between two concepts or two aspects of something; a dualism.
duplex: (North American) a house divided into two apartments, with a separate entrance for each. This kind of house is quite common in one area of the Edison Township.
bilateral: having or relating to two sides; affecting both sides. For example, “bilateral talk”.
bipartisan: involving the agreement or cooperation of two political parties that usually oppose each other’s policies.
bifocal: a pair of eyeglasses having lenses with two parts with different focal lengths. My friend has a pair of bifocal glasses.
binary: relating to, composed of, or involving two things. For example, computer is using a binary system to count.
boolean: a binary variable, having two possible values called “true” and “false.”.
Phrases Contain “Two“
There are a lot of phrases that have “two”, but I’ve only listed several that I’ve seen being used pretty often. If you have any other phrases, please leave me a comment.
kill two birds with one stone: achieve two aims at once.
serve two masters: take orders from two superiors or follow two conflicting or opposing principles or policies at the same time. I often feel that women who juggle work and home life are serving two masters.
two peas in a pod: so similar as to be indistinguishable or nearly so.
give one’s two cents: To share one’s opinion or point of view for whatever it may be worth, generally when it is unasked for.
lesser of two evils: the less harmful or unpleasant of two bad choices or possibilities.
not care two straws about someone or something: to attach no importance to someone or something
the evil twin: An identical twin or unrelated person who has a similar appearance to a decent or moral person but who wreaks havoc or does evil.
It takes two to tango: The phrase is used when you want to emphasize that both people involved in a difficult situation must accept the blame.
a bird in the hand is worth two in the bush: it’s better to be content with what you have than to risk losing everything by seeking more.
to bring someone down a peg or two: to make someone who is behaving in an arrogant and unpleasant way realize that they are not as important or talented as they think. “I do think he needed taking down a peg or two.”
put two and two together: to make a correct guess based on what one has seen or heard.