IPA: /ˈwɜːrliər/
KK: /ˈhwɜrliər/
Having a spinning or rotating motion; characterized by a whirling movement.
The whirlier the leaves, the more beautiful the autumn scene becomes.
Comparative: whirlier
Superlative: whirliest
Whirlier is formed from "whirl" (of uncertain origin, possibly imitative of the motion) and "-ier" (a suffix used to form comparative adjectives). The word "whirlier" means more characterized by a spinning or rotating motion than something else.
Think of something that spins or rotates more than another — that's what 'whirlier' describes.