Thirsty means needing a drink, so your mouth feels dry. Feel thirsty, thirsty work, get thirsty.
Thirst is a late signal — by the time it arrives the body has already lost fluid — which is why athletes and workers in heat are told to drink to a schedule rather than to thirst. Thirsty work is a fixed phrase, usually said hopefully. Note thirst; and that the word is Old English and Germanic.
1adjectivethirstyNeeding a drink.
“After running in the heat, I was so thirsty that I drank a whole bottle of water.”
thirsty is a state of need.
Old English thurstig is thirst plus -y. Thirst comes from a Germanic root also connected with dryness.
Proto-West Germanic
*þurstug
Old English
þurstiġ
Middle English
thirsty
English, today
thirsty
From Middle English thirsty, from Old English þurstiġ, from Proto-West Germanic þurstug. Equivalent to thirst + -y. Cognate with Dutch dorstig, German durstig.
Etymology from Wiktionary, CC BY-SA