A repeat unit: a structural unit which through repetition forms a polymer.
"The sailors whispered about seeing merpeople dancing beneath the moonlit waves."
merpeople
In plain English: A mer is an imaginary creature from folklore that looks part human and part fish, often living underwater with long hair and a tail instead of legs.
"The kids spent their summer vacation playing in the warm mer near our house."
Usage: In chemistry, a mer refers to the single repeating molecular unit that makes up a larger polymer chain when many are linked together. Use this term specifically in scientific contexts describing synthetic materials like plastics or fibers rather than general language about parts or sections.
Initialism of Mars Exploration Rover.
"The MER mission successfully explored two rocky worlds on opposite sides of our solar system."
The word mer is a clipping of the term polymer. It originally referred to a repeating unit within a polymer chain.