The term "stolen base" is a quintessential American baseball idiom from the mid-19th century. It is a straightforward compound noun, literally describing the act of "stealing" a "base." The logic is transparent: the runner, like a thief, takes possession of the base through cunning and speed without the ball being put into play, an action initially considered unsporting. The metaphorical extension of "stealing" something valuable through stealth or trickery aligns perfectly with the Germanic root of 'steal', related to notions of theft and secrecy. The classical root of 'base', from Greek 'basis' (a step, foundation), evolved through Latin and French into its sporting sense as a safe station or goal, completing the vivid image of illicitly acquiring a position.

Structure: stolen (past participle of 'steal') + base (a station or goal) - stolen: From Old English 'stelan' (to steal), of Germanic origin. In this compound, it functions as a participial adjective modifying the noun 'base'. - base: From Old French 'bas', from Latin 'basis' (foundation, pedestal), from Greek 'basis' (a stepping, step, base). In this compound, it functions as a noun meaning the specific station or objective in the game of baseball.