虚
xū · HSK 7
empty or unoccupied
🕳️ xū sounds like shh — a hush so total the space is empty, a void
The 虍 tiger radical sits on top of an old word for a big empty mound. The empty sense carries into 谦虚 (modest = empty of arrogance) and 虚弱 (weak = drained, hollow). Abstract theory is empty in the sense of having no physical body.
虚 — tiger radical 虍 + hill 丘 (now 业)
Originally depicted a large mound or hill where tigers (虍) roamed, written with 虍 over 丘. Because such high places were often deserted, the meaning shifted from 'big hill' to 'empty, void, vacant,' and by extension 'unreal' or 'humble.' The bottom 丘 was later simplified to 业.