The word "top-notch" is a compound adjective formed from two common English nouns. "Top," of Old English origin, has always signified the highest point or peak. "Notch," from Old French, originally referred to a V-shaped cut, often used as a tally mark on a stick to record scores or levels. The phrase likely originated in the 19th century from the practice of using notches to indicate quality grades, with the highest grade being at the top of the scale. The literal image of the highest notch on a measuring stick evolved into a figurative expression for anything considered first-rate or superior.

Structure: top (highest part) + notch (cut, level) - top: From Old English 'topp' (summit, crest). In this compound, it functions as an intensifier meaning "highest" or "best." - notch: From Anglo-French 'noche' (a nick, groove). In this compound, it functions metaphorically as a marker or grade of quality.