thumb
Preserved but no longer current.
Meaning · English
By rule of thumb: to do any thing by dint of practice. To kiss one's thumb instead of the book; a vulgar expedient to avoid perjury in taking a false oath.
Era: ca. 1811 (Georgian)
Where it’s used:
Origin
British & Irish English
Sources & notes
Historical definition reproduced from Grose’s Dictionary of the Vulgar Tongue (1811 edition, public domain; Project Gutenberg #5402, retrieved 2026-07-31). Reflects the attitudes of its era.
Common questions
What does “thumb” mean?
By rule of thumb: to do any thing by dint of practice. To kiss one's thumb instead of the book; a vulgar expedient to avoid perjury in taking a false oath.
Is “thumb” formal or informal?
No register label has been reviewed yet — treat it as neutral and check the usage notes above.