The word "咳痰" is formed by combining the character "咳", meaning to cough, which uses the mouth radical (口) to indicate an action involving the mouth and the phonetic component "亥" for sound, with the character "痰", meaning phlegm, which uses the illness radical (疒) to signify a medical aspect and the phonetic component "炎" for sound; together they create a compound that literally denotes the action of coughing up phlegm.