* Formal: The difference between the two values was infinitesimal, practically negligible.
* Informal: The chance of winning the lottery is infinitesimal, but people still dream.
* Figurative: Her patience wore thin, eroding by infinitesimal degrees with each passing hour.
* Technical: Calculus uses infinitesimals to study changes in functions over incredibly small intervals.
Remember that "infinitesimal" refers to something incredibly small, almost impossibly so.