IPA: /ʌnˈwaɪzər/
KK: /ʌnˈwaɪzər/
Not showing good judgment or sense; lacking wisdom.
His decision to invest in that failing company was unwiser than I expected.
Unwiser → It is formed from "un-" (meaning not) and "wise" (from Old English "wīs", meaning having knowledge or good judgment). The word "unwiser" means not having wisdom or being less wise than before.
Think of 'not' ('un-') being added to 'wise' — this helps you remember that 'unwiser' means lacking wisdom.