Infinitesimal :: Infinitesimal (a.) Infinitely or indefinitely small; less than any assignable quantity or value; very small.
Infinitesimal :: Infinitesimal (n.) An infinitely small quantity; that which is less than any assignable quantity.
Infinitesimally :: Infinitesimally (adv.) By infinitesimals; in infinitely small quantities; in an infinitesimal degree.