What does 骨头 (gǔ tou) mean in English?

Card 352HSK 2010 Level 5352/1311
CARD352
PROGRESS27%
骨头
骨頭
gǔ tou
bone; strong character; CL:根[gen1],塊|块[kuai4]
Click to reveal
← Previous↑ DeckNext →

Reveal: Click/Space/Enter/↑↓/w/s/j/k•Navigate: ←→/h/l/a/d