Long in the Tooth

The Definition

A polite (or sometimes slightly disparaging) way of saying that someone or something is getting old. It suggests that a person is past their prime or has been around long enough to be considered a "veteran" of their particular field or era.

The Deep Dive

The "junk knowledge" behind this phrase is the biological reality of how horses age. Unlike humans, whose teeth reach a fixed size and then slowly wear down or fall out, a horse's teeth continue to erupt from the gums throughout most of its life.

In the days before birth certificates for livestock were standard, a horse trader or a farmer had to rely on physical clues to determine the age of an animal.

  • The Gum Recession: As a horse ages, its gums naturally recede, and the physical crown of the tooth appears to get longer. Additionally, the angle at which the upper and lower teeth meet becomes more slanted over time.

  • The "Tooth" Test: By pulling back a horse's lips and examining the length and angle of the incisors, a buyer could accurately estimate if the horse was a young, vigorous worker or "long in the tooth"—an old nag that might be nearing the end of its usefulness.

The phrase migrated from the stables to the Victorian social circle in the mid-1800's. It was famously used by authors like William Makepeace Thackeray to describe aging aristocrats who were trying to maintain their youthful appearance despite their obvious seniority. It represents the "junk" of the pre-industrial world: a diagnostic tool for livestock that became a permanent metaphor for human mortality.

Fast Facts

  • Don't Look a Gift Horse: This is the sister idiom to "Long in the Tooth." Looking a "gift horse" in the mouth was considered rude because you were checking its teeth to see exactly how old (and therefore how "cheap") the gift actually was.

  • The Galvayne’s Groove: Real "horse-tooth experts" look for a specific dark line called Galvayne’s Groove, which appears on the upper corner incisor at age 10 and reaches the bottom of the tooth by age 20.

  • The Human Exception: While we use the phrase for people, human teeth don't actually get longer as we age; our gums simply recede due to age or wear, creating a similar visual effect that keeps the metaphor biologically resonant.

References

  • Thackeray, W. M. (1852). The History of Henry Esmond. (Early literary use of the phrase).

  • Youatt, W. (1831). The Horse. (A classic veterinary text on aging horses by their teeth).

  • Ammer, C. (2013). The Dictionary of Clichés. Skyhorse Publishing.

  • The Oxford English Dictionary. (2026). Tooth (n.). Oxford University Press.