once-a-week

The term 'once-a-week' is a modern English compound that transparently combines common temporal words. 'Once' originates from the Old English ānes, meaning 'one time', which itself derives from the numeral ān (one). The indefinite article 'a' evolved from the Old English preposition on, used here in its sense of 'per' or 'each'. 'Week' comes from the Old English wice, related to a Germanic root meaning 'a turning' or 'succession', referring to a cycle of days. The logic of the compound is entirely literal, directly encoding its meaning of a single occurrence within each weekly cycle, a pattern typical of English's analytic method for creating specific frequency descriptors.

This is a hyphenated compound phrase formed from three standard English words. 'Once' (from Old English ānes, genitive of ān 'one'), 'a' (a reduced form of the Old English preposition on), and 'week' (from Old English wice, wicu). The phrase functions as a single lexical unit, an adjectival or adverbial compound.