Thirstiness is from thirsty (Old English thurstig) + the abstract-noun suffix -ness, ultimately from thurst ('thirst'). Important recorded forms include thurstig (Old English) and thurst (Old English). Morphologically, the native -ness suffix turns an adjective or quality word into an abstract noun naming the state or condition. The modern sense is largely compositional, with the historical elements narrowing into a stable English lexical item. In current use it covers the state of being thirsty. The wider family includes related words such as thirsty, thirst, and thirsting.