đầu gối

đầu (“head”) +‎ gối (“knee”), perhaps to avoid ambiguity with the other gối (“pillow”), but also probably to refer specifically to the "head" of the knee, the kneecap (compare English olecranon (literally “head of the elbow”)). Sino-Vietnamese đầu largely displaced native trốc, as in trốc gối.

For some semantic parallels, compare Thai หัวเข่า (hǔua-kào), Zhuang gyaeujhoq, Chinese 膝頭／膝头 (tất đầu), Japanese 膝頭 (hizagashira), Ainu コッカサパ (kokkasapa), Malay lutut, Basque belaunburu, Welsh pen-lin, Yoruba orunkun.

• (Hà Nội) IPA^(key): [ʔɗəw˨˩ ɣoj˧˦]
• (Huế) IPA^(key): [ʔɗəw˦˩ ɣoj˨˩˦]
• (Hồ Chí Minh City) IPA^(key): [ʔɗəw˨˩ ɣoj˦˥]

đầu gối

1. knee (joint in the middle of the leg and area around it)

   Synonym: gối