The word '半瓶醋' is formed by combining the character 半 (half) with 瓶 (bottle) and 醋 (vinegar), creating a literal meaning of 'half a bottle of vinegar.' This phrase serves as an idiomatic expression where the literal image is used metaphorically to describe someone with superficial knowledge, derived from the concept of a container not being full. The formation involves a quantifier modifying a noun phrase, resulting in a compound that conveys this figurative sense through its direct structural composition.