The word "手指头" is a compound noun formed through morphological construction, combining the root "手" (shǒu, hand) with the specific term "指" (zhǐ, finger) and adding the colloquial suffix "头" (tou), which is commonly used in spoken Chinese to form familiar, concrete nouns without altering the core meaning. Thus, "手指头" literally and functionally means "finger", where "手" specifies the location (on the hand), "指" denotes the object itself, and "头" provides a casual, tangible nuance, resulting in a word that is more everyday and descriptive than the simpler "手指".