the.com/middleweight

means A boxing and martial arts weight division for fighters roughly in the middle of the scale — historically around 154 to 160 pounds — too heavy for welterweight, too light for light heavyweight.

from Straightforward compound English — 'middle' plus 'weight' — coined as boxing formalized its weight classes in the 1800s. The sport originally just had heavyweights and lightweights; as rules and sanctioning bodies multiplied, promoters carved out finer gradations to make matches fairer, and 'middleweight' slotted in as the obvious name for the class sitting between the two extremes.