Is Infinitesimal a Real Word?

indefinitely or exceedingly small; minute: infinitesimal vessels in the circulatory system. immeasurably small; less than an assignable quantity: to an infinitesimal degree.

Do Infinitesimals exist?

Infinitesimals were introduced by Isaac Newton as a means of “explaining” his procedures in calculus. Before the concept of a limit had been formally introduced and understood, it was not clear how to explain why calculus worked. Hence, infinitesimals do not exist among the real numbers. ...

Where does the word infinitesimal come from?

The word infinitesimal comes from a 17th-century Modern Latin coinage infinitesimus, which originally referred to the "infinity-th" item in a sequence.