lightweight

nouns

a professional boxer who weighs between 131 and 135 pounds
is a type of (narrower)
a professional boxer
someone who is unimportant but cheeky and presumptuous
an amateur boxer who weighs no more than 132 pounds
is a type of (narrower)
someone who fights with his fists for sport
a wrestler who weighs 139-154 pounds
is a type of (narrower)
combatant who tries to throw opponent to the ground

adjectives

weighing relatively little compared with another item or object of similar use
"a lightweight fabric"; "lightweight wood"
is similar to
of comparatively little physical weight or density
"a light load"; "magnesium is a light metal--having a specific gravity of 1.74 at 20 degrees C"
having no importance or influence
"a lightweight intellect"
is similar to
not important
"a relatively unimportant feature of the system"; "the question seems unimportant"