decade
Because the prefix 'deca' means ten. A decagon has ten sides - a decade is ten years.
A decagon will always have 10 sides. The prefix deca- means 10, so its inclusion before a word will always carry that meaning.
decade
Deca-, from the Greek deka, is a prefix meaning ten. Decem is the Latin word for ten
The word, "Decagon" must have ten sides. Its beginning, "Deca", is Latin for ten.
One word, which means a 10-sided shape, is decahedron. Another word beginning with "deca" is decade, meaning 10 years.
The prefix "dec" means ten. For example, the word "decagon" refers to a ten-sided polygon.
Deci- is a prefix which is used to mean "one tenth" - for example, a decimetre is a unit of length equal to one tenth of a metre. Also, interestingly, the original meaning of the word "decimate", nowadays meaning "to eliminate in large numbers" originally meant, when referring to Roman soldiers, to "kill one in every ten". Deca- is a prefix which is used to mean "ten" - using a similar example, a decametre is a unit of length equal to 10 metres. Other words using the prefix deca- include decagon - a ten-sided polygon, and decapod - a ten-legged object.
deci- is a tenth. Decimal, decimate, December (originally the tenth month)...
The prefix deka- (and the related form deca) come from Greek, meaning "ten."
How about a decagon which is a ten sided polygon
Nonagon is a word that begins with the prefix "non" and means a polygon with nine sides.