humectant
Any substance that promotes the retention of water, especially one used to keep a food product moist.
[…] that you have induced a horrid phlegmatic condition with will soon require a liberal and generous humectant to keep the very membranes of your very entrails from desquamating, chipping off and blocking up all the pipes of your body.
Where it comes from
From Latin ūmectāns, present participle of ūmectō (“to moisten”), from ūmectus (“moist”), from ūmeō (“to be moist”).
Adapted from the Wiktionary entry humectant (CC BY-SA 4.0).