The word "拇指" is formed by combining the character "拇", which specifically means thumb, with the character "指", which means finger, resulting in a compound that directly denotes the thumb as a digit. Both characters use the hand radical ("扌") to indicate relation to the hand, while their phonetic components ("母" in "拇" and "旨" in "指") suggest pronunciation, but the formation is primarily semantic, merging a specific term with a general one to specify the body part.