IPA: /ˌpriːdɪˈmɪnər/
KK: /prɪˈdiːtərˌmɪnər/
A type of word that comes before a determiner in a noun phrase, often used to quantify or limit the noun, such as 'both' or 'all'.
In the sentence 'Both the cats are sleeping', 'both' is a predeterminer.
Predeterminer → It is formed from "pre-" (meaning before) and "determiner" (from Latin "determinare", meaning to limit or define). The word "predeterminer" refers to a word that limits or defines a noun before the main determiner is used.
Think of something that defines or limits a noun 'before' ('pre-') the main determiner is used — that's what a predeterminer does.