Illustrated Glossary of Organic Chemistry

Aromatic overtones: In infrared spectroscopy, a series of small peaks (usually three or four) typically found in the ~2000 cm-1 to ~1700 cm-1 range. Caused by overtones (harmonics) of the benzene ring vibrational modes having stretching frequencies in the infrared spectrum's fingerprint region.

In this infrared spectrum of toluene, there are four aromatic overtone peaks.