The compound noun 'three-pack' is a modern commercial formation, transparently combining the numeral 'three' and the noun 'pack'. 'Three' descends from the Proto-Indo-European root tréyes, a fundamental numeral that gave rise to its equivalents across Indo-European languages, including Latin trēs and Greek treis. 'Pack' entered English from Low German dialects, carrying the core meaning of a bundle or parcel. The logic of the compound is purely descriptive, following the common English pattern of number-noun compounds to denote a standardized retail unit containing a specific quantity of items.

Structure: three (numeral) + pack (noun) - three: From Old English þrīe, þrēo, of Proto-Germanic origin; related to Latin trēs, Greek treis. Functions as a numeral root specifying quantity. - pack: From Middle Dutch pac or Middle Low German pak, of uncertain ultimate origin, possibly related to the concept of bundling. Functions as a noun root meaning a bundle or package.