A person who rollerskates or inline skates; someone who participates in the sport or activity of rollerblading.
From 'blade' (the wheels on rollerblades) + '-er' (agent suffix). Modern coinage from the 1980s-90s as the sport of inline skating developed.
The word 'blader' arose from street culture and became mainstream just as inline skates revolutionized wheeled sports—it's a perfect example of how new technologies create new words to describe new communities!
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