One object holds this whole word: two rounded glass halves together at a narrow neck, with sand falling through. Two things about it can be borrowed. The shape - wide, narrow, wide - and the message the falling sand sends: time is passing and you can only wait. Every meaning here takes one of those two.
From the word’s history
The packet's source gives the word as simply hour plus glass: the glass thing that measures an hour. That literal build is still visible in the object, and it explains why small three-minute timers keep the name even though they do not run for an hour.
這份資料的來源說，hourglass 就是 hour 加 glass：量一個小時的玻璃器。這個字面組合到今天還看得出來。也因為名字綁的是那個東西，三分鐘的小沙漏一樣叫 hourglass，並不會因為跑不到一小時就換名字。
Wiktionary 'hourglass' etymology as supplied in this packet: From hour + glass (source_ref kaikki:3f6f69a190036ae4:88167758)
登入就可以看每一支怎麼連回核心畫面。