how many?

a couple--2--of anything, or 2 people who are an "item"--sometimes called a "pair"

duo or duet--2 performers
trio--3 performers

twins--2 siblings born at one time
triplets--3 siblings born at one time

quartet--4 performers
quintet--5 performers--(these go on in number, even if people once invented a new word for them-sextet, septet, octet)

decade--10 years

dozen--12 of something--eggs or doughnuts, or anything else
half-dozen or "half a dozen"--6 of something

a "score"--an old-fashioned word for 20--"four score and seven years ago", spoken in 1863, meant 1776 (1863-87=1776)

century--a hundred years, or defining a particular century by the number of its years--as today, we live in the 21st century

a gross--a business term for 12 dozen, or 144

triangle--a 3 sided shape--as in a "yield" sign
"quad" or quadrangle-a 4 sided shape, hence a public court or square
pentagon--5 sided shape--the Pentagon in Washington, DC has 5 sides
hexagon--6 sided shape--some quilts or old-fashioned floor tiles are hexagons
octagon--8 sided shape--as in a stop sign-different shapes make the signs easier to see quickly

a quarter--1/4 (of a dollar), or of anything else--1/4 is what you get when you divide something in 4 parts
a quarter to 12 is 11:45, or 15 minutes (a quarter of an hour) before 12
half is what you get when you divide something in 2--so half an hour is 30 minutes

All of the words above mean a specific number--although we agree on what, or how many, "a few" is, or "several", they are vague--they don't mean an exact number--an approximation will do.