¦riktə(r)- noun
Usage: usually capitalized R
Etymology: after Charles F. Richter died 1985 American seismologist
: an open-ended logarithmic scale for expressing the magnitude of a seismic disturbance (as an earthquake) in terms of the energy dissipated in it with 1.5 indicating the smallest earthquake that can be felt, 4.5 an earthquake causing slight damage, and 8.5 a very devastating earthquake