四分之三 means 'three quarters' or 'three fourths' and is used as a quantifier before nouns to indicate a fraction of a whole. It follows the pattern 'number + 分之 + number', where 分 marks the parts and 之 is a possessive particle. Although the POS in the source data lists it as a measure word, it functions more naturally as a noun phrase that modifies the following noun, similar to 'half (一半)'.