Proverbial means well known from a common saying. The proverbial needle, proverbial patience, the proverbial last straw.
It is used to flag that a phrase is a set one, which lets a writer use a cliche while pointing at it: the proverbial needle in a haystack. Nobody says proverbial about a saying they have just made up, which is the whole point of the word.
1adjectiveproverbialWell known from a common saying.
“Finding my ring in the long grass was like looking for the proverbial needle in a haystack.”
proverbial is a quality.
Latin proverbialis comes from proverbium, a proverb — pro, forth, plus verbum, a word.
Latin
prōverbiālis
English, today
proverbial
From Latin prōverbiālis, equivalent to proverb + -ial
Etymology from Wiktionary, CC BY-SA