thumb hook（拇指钩）是什么意思？音标发音+图解场景

拇指钩 /ˈθʌm ˈhʊk/ n

English: thumb hook · 拇指钩

释义：Part in which the thumb is inserted to lengthen the first valve slide and tune certain notes while playing.

这个词出现在以下图解场景（1）