What part of the speech is "two"?

What part of the speech is the word "two"? Since it denotes the number, it is logical to assert that "two" is a quantitative numeral. But when answering the question about what part of the speech is "two", it should be noted that the numeral is not quite ordinary. Along with their brethren, the words "both" and "one and a half," the numeral "two" has a morphological form of the genus. Simply put, the words "two", "one and a half" and "both" indicate the grammatical kind of nouns that are with them in the pair.

Compare:

• two apples, two buttons;
• one and a half ruble, one and a half spoons;
• both eyes; both girls.

But:

• Four pears, four boys;
• Ten cars, ten cows;
• Six tracks, six chairs.