Definition of "mer"

A polymer is a compound formed of repeating structural units called mers, whose atoms share electrons to form very large molecules.

2010, Mikell P. Groover, Fundamentals of Modern Manufacturing (4th Edition), page 9

There are mermaids and mermen everywhere. They swim above us and linger in nooks and arched doorways. It's impossible not to stare. The mer are as diverse as humans—all ages, size, shape, and color.

2013, Missy Fleming, Into the Deep, page 65