Illustrated Glossary of Organic Chemistry

Singlet: In NMR spectroscopy, a signal which is not split; i.e., it is a single line.

This simulated ¹H-NMR spectrum of 2-ethylphenol includes a multiplet at 6.6-7.2 ppm, a singlet at 6.0 ppm, a quartet at 2.4 ppm, and a triplet at 1.2 ppm. Click on the image for a larger version.