The term 'prefix denoting 'EIGHT'' refers to words that begin with a certain combination of letters that signify the number EIGHT. The two crossword solutions for this term are 'octo' and 'octa, ' both of which have four letters. 'Octo' is derived from the Latin word for EIGHT, 'octo, ' while 'octa' is derived from the Greek word for EIGHT, 'okto.' Both words are used in various contexts to refer to the number EIGHT.