Something that is so small as to be almost negligible.

अति सूक्ष्म मात्रा

English Usage: The physicist calculated the effect of infinitesimal charges on the electric field.

Hindi Usage: भौतिक शास्त्री ने इलेक्ट्रिक फील्ड पर अति सूक्ष्म चार्जेस के प्रभाव की गणना की।