Origin: Germanic Old English suffix
Lightweight has 8 different meanings across 2 categories:
a professional boxer who weighs between 131 and 135 pounds
"After years of training, he finally stepped into the ring as a lightweight contender."
someone who is unimportant but cheeky and presumptuous
"The lightweight editor made bold claims about the company's future despite having no real authority or influence."
an amateur boxer who weighs no more than 132 pounds
"After winning his regional tournament, the lightweight moved up to challenge for a national title."
a wrestler who weighs 139-154 pounds
"After years of training, he finally qualified as a lightweight in his first professional wrestling match."
A particular weight class, or member of such, as prescribed by the rules, between that of the heavier welterweight and the lighter featherweight. See Wikipedia for the specifics of each sport.
"The boxer stepped onto the scale to confirm he was a lightweight before his championship match against the welterweight contender."
In plain English: A lightweight is someone who isn't very serious about things and often makes silly decisions easily.
"The lightweight won the boxing match with ease."
Usage: As a noun referring to boxing, lightweight describes a specific weight class situated between welterweight and featherweight. In everyday conversation, this term is often used more broadly for any person or object that is notably small or light compared to others in its category.
weighing relatively little compared with another item or object of similar use
"a lightweight fabric"
"lightweight wood"
Lacking in earnestness, ability, or profundity
"The author's latest novel was criticized as a lightweight effort that lacked any real depth or insight into human nature."
In plain English: Lightweight means something that is very light and easy to carry around.
"He prefers lightweight furniture that is easy to move around his small apartment."
The word lightweight is a compound formed from the words light and weight. It was first used to describe something that has little mass or physical heaviness.