| femtochemistry | (n) the branch of chemistry that studies elementary (often very fast) chemical reactions as they occur; the experimental methods are often based on the use of femtosecond laser pulses |
| femtometer | (n) a metric unit of length equal to one quadrillionth of a meter, Syn. fermi, femtometre |
| femtosecond | (n) one quadrillionth (10^-15) of a second; one thousandth of a picosecond |
| femtovolt | (n) a unit of potential equal to one quadrillionth of a volt (or one thousandth of a nanosecond) |