희소해요 · 희소했어요 · 희소한 (+noun)
rare, scarce
Example
희소한 자원일수록 가격이 비싸요.
The scarcer a resource is, the more expensive it is.
Word parts
희 rare+소 few
Literally 'rare and few'.
Good to know
희소성 'scarcity value' comes up often in economics and marketing.
Related words