kiddo

The word "kiddo" is a modern, informal English coinage. Its first element, "kid," has origins in Middle English, where it referred to a young goat, possibly from Old Norse "kið." By the late 16th century, "kid" had developed its slang sense for a child. The appended "-o" is a colloquial suffix used to form familiar, often affectionate, nicknames and terms of address, as seen in words like "jacko" or "matey-o." Therefore, "kiddo" literally constructs a sense of "little kid" or "young one," but its function evolved specifically into a term of friendly address, blending familiarity with a hint of endearment or gentle condescension.

This word is a simplex formation. It is a colloquial alteration of the English word "kid," meaning a child or young goat, combined with the affectionate or familiar suffix "-o," a common feature in informal English and Australian slang.