IPA: /ˈsiːmliːst/
KK: /ˈsimlɪst/
The most appropriate or proper in behavior or appearance.
At the formal event, she wore the seemliest dress that impressed everyone.
Comparative: more seemly
Superlative: seemliest
Seemliest is formed from "seem" (from Old English "seman", meaning to appear or to be perceived) and the suffix "-liest" (a superlative suffix indicating the most). The word "seemliest" means the most pleasing or agreeable in appearance.
Think of the word 'seem' which relates to how something 'appears' — and the '-liest' tells us it's the most pleasing appearance.
No commonly confused words.