The compound noun "tie-in" is a modern formation from the phrasal verb "to tie in," which emerged in American English in the early 20th century. The core verb "tie," with its Old English origin meaning to bind or fasten, provides the fundamental concept of connection. The adverbial particle "in" adds the nuance of integration, suggesting a link that brings separate elements into a unified or related system. This logical combination of "binding into" evolved from its literal sense (e.g., tying a horse into a train of wagons) to its dominant modern, abstract commercial meaning, denoting a promotional or narrative link between products, media, or ideas.

Structure: tie (bind) + in (inclusion) tie: From Old English tīgan, meaning "to bind". It functions as the core verb root indicating connection. in: From Old English in, a preposition/adverb. It functions as a particle modifying the verb, indicating inclusion or integration into a larger context.