The compound "summer-league" is a modern American English formation that transparently combines two established nouns. "Summer," a word of ancient Germanic descent referring to the warmest season, specifies the temporal scope. "League," with its origins in the Latin verb ligare (to bind), denotes an association bound together by a common purpose, such as sports competition. The term's logic is entirely literal, describing a sports league that operates specifically during the summer months. Its secondary, metaphorical sense of something amateurish or developmental derives from the perception of these leagues as preparatory and less prestigious than the primary professional seasons.

Structure: summer (season) + league (association) - summer: From Old English sumor, of Germanic origin; related to Dutch zomer and German Sommer. Functions as a noun specifying the time period. - league: From Middle English ligg, via Old French ligue and Italian lega, from Latin ligare meaning 'to bind'. Functions as a noun meaning an association or alliance for a common purpose.