‘闷头’ is an adverbial phrase meaning 'stubbornly, silently, or without speaking up'—it describes doing something in a withdrawn, sullen, or uncommunicative way. The character 闷 (mēn) conveys suppression, stifling, or emotional constriction (as in 闷气, 'to hold in anger'), while 头 (tóu) here functions as a noun suffix that adds a sense of direction or manner—similar to how it appears in phrases like 埋头 ('bend one’s head', i.e., 'diligently concentrate'). Together, 闷头 evokes the image of someone with their head down and mouth shut, persisting inwardly without explanation or interaction.

This expression often carries a slightly negative or empathetic nuance: it may suggest quiet resentment, stubborn determination, or emotional withdrawal—not mere silence, but silence paired with action or resistance. It commonly modifies verbs like 干 (do), 想 (think), or 走 (walk), and appears frequently in spoken Mandarin, especially when describing reactions to criticism, disappointment, or pressure.