Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
deca-, dec-, deci- (prefixes)
All three prefixes involve the number ten. Pronounce the first two DEK-uh- and DEK-, respectively; they both mean “ten times.” Deca- combines with bases beginning with consonants, as in decagon, “a polygon that has ten sides and ten angles”; dec- combines with bases beginning with vowels, as in decathlon (only three syllables), “an athletic event in which performers each compete in ten different events.” Deci- is pronounced DES-i- or DES-uh- and means “one-tenth”—A deciliter is “one tenth of a liter.”
