ballpark

The word "ballpark" is a transparent compound formed from two common English nouns, "ball" and "park." Its literal meaning, originating in the late 19th century, simply denoted a field or stadium designed for playing ball games, most notably baseball in American English. The crucial semantic shift occurred in the mid-20th century, where the term began to be used metaphorically. The logic stems from the idea of a baseball park as a defined, bounded area; thus, giving a "ballpark figure" means providing an estimate that falls within acceptable, though not precise, boundaries. This evolution from a concrete sports venue to an abstract concept for approximation showcases a classic path of semantic extension based on the conceptual frame of a defined space.

Structure: ball + park - ball (Old English beall, meaning a round object for play or sport; the noun in this compound) - park (Old French parc, Medieval Latin parricus, meaning an enclosed piece of ground; the noun in this compound)