IPA: /ˈsmaɪliər/
KK: /ˈsmɪliər/
Having a more cheerful or friendly expression than usual.
She looked even smilier after receiving the good news.
Comparative: smilier
Superlative: smiliest
Smilier is formed from "smile" (from Old English "smīel", meaning to smile) and the suffix "-ier" (indicating a comparative form). The word "smilier" means more inclined to smile or having a greater tendency to smile than something or someone else.
Think of someone who is more inclined to 'smile' — the suffix '-ier' indicates a comparison, so a 'smilier' person smiles more than others.