so-and-so
UK[ˈsəʊ ən ˌsəʊ]US[ˈsoʊ ən ˌsoʊ]
n
A person or thing whose name is not specified or is not known
n
A person or thing regarded as mediocre, ordinary, or unimpressive
Etymology
The term "so-and-so" is a reduplicative compound, a pattern common in English for creating indefinite or placeholder terms. It emerged in the late 16th century, built from the simple, flexible adverb "so," which has Old English and Germanic origins meaning "in this way" or "to this extent." The repetition "so and so" mimics the structure of a name being given (e.g., "Mr. So and So") while deliberately withholding specific identity. Over time, its meaning expanded from a mere anonymous placeholder to often carry a mild, dismissive connotation, referring to someone or something considered unremarkable or vaguely disagreeable.
Analysis
This is a fixed compound formed by the repetition of the common English word "so". It functions as a placeholder or dummy noun.
Examples
The form asked me to contact Mr. So-and-so in the accounting department.
She said she was meeting a so-and-so for lunch but didn't mention who.
He's just another so-and-so trying to sell you something you don't need.