The definition of infinitesimal is something extremely small or very close to 0, or too small to be measured.(adjective)
When you have only a single grain of rice, this is an example of a time when you have an infinitesimal amount of rice.
See infinitesimal in Webster's New World College Dictionary
Origin: ModL infinitesimus < L infinitus (see infinite), infl. by centesimus, hundredth < centum, hundred
See infinitesimal in American Heritage Dictionary 4
Origin: From New Latin īnfīnītēsimus, infinite in rank
Origin: , from Latin īnfīnītus, infinite; see infinite.
Learn more about infinitesimal