IPA: /ˈsnʌɡər/
KK: /snʌɡər/
More tight-fitting or comfortable than something else.
This sweater is snugger than the one I wore yesterday.
Snugger is derived from the word "snug" (of uncertain origin, possibly from Old Norse "snuggr", meaning tight or comfortable) with the comparative suffix "-er" (indicating more). The word "snugger" means more snug or more comfortable than something else.
Think of something being 'tighter' or 'more comfortable' — that's what snugger means.