Any substance that is added to another substance to keep it moist

Wiktionary Word definitions in Wiktionary
n. any substance that promotes the retention of water, especially one used to keep a food product moist

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Humectant \Hu*mec"tant\, a. [L. humectans, p. pr.] Diluent. -- n. A diluent drink or medicine. [Obs.]

WordNet Word definitions in WordNet
n. any substance that is added to another substance to keep it moist

Wikipedia Word definitions in Wikipedia
A humectant is a hygroscopic substance used to keep things moist; it is the opposite of a desiccant . It is often a molecule with several hydrophilic groups, most often hydroxyl groups ; however, amines and carboxyl groups , sometimes esterified , can be ...