thirsty: in need of water and craving it, whether a person longing for a drink or ground parched for rain
This word is an adjective describing the state of lacking water and wanting it. In a dry land, thirst was a matter of survival, so calling someone "thirsty" was never trivial. It named real danger: the failing strength of travelers in the wilderness, of prisoners, of the poor whose drink runs out.
From that vivid physical picture the word stretches naturally into a comparison. Cracked, dry ground is "thirsty" for rain, and a person can be thirsty for God the way parched land longs for water (Isaiah 55:1). Because English keeps the very same image, these figurative uses read just as cleanly for us as the literal ones.
Its sibling noun צָמָא names the thirst itself, the condition, while this word describes the one who has it. The New Testament reaches for the same picture with the Greek verb διψάω, which likewise runs from a literal dry throat to a deep longing for God.