The expression originates from the Old English phrase "þanc þē," where "þanc" (later 'thank') meant 'thought, good will, gratitude' and "þē" is the dative singular of the second person pronoun. Over centuries, the phrase grammaticalized from a literal statement ("I give you thanks/thought") into a fixed polite formula. Its spelling solidified as a hyphenated compound noun and adjective in the 18th and 19th centuries, reflecting its use to denote a concrete acknowledgment of gratitude, such as a note or gift. The evolution from a verbal phrase to a lexicalized unit exemplifies how common expressions can become fossilized as single conceptual entities in the language.

The term is a fixed compound or phrasal noun formed from the verb phrase "thank you." It is not productively segmented into smaller, independent morphemes in its current conventionalized form.