IPA: /ˌæntiˈdɛsɪkənt/
KK: /æntiˈdɛsɪkənt/
A substance that prevents drying out or loss of moisture.
The antidesiccant helped keep the plants hydrated during the dry season.
A substance that stops things from drying out.
The farmer used an antidesiccant to keep the crops hydrated during the dry season.
Antidesiccant is formed from "anti-" (meaning against) and "desiccant" (from Latin "desiccans", meaning drying). The word refers to a substance that works against drying out or moisture loss.
Think of 'against' ('anti-') something that 'dries' ('desiccant') — that's why antidesiccant means a substance that prevents drying.