IPA: /ˈlɛŋθiər/
KK: /ˈlɛŋθiˌɚ/
This word describes something that is longer in duration or extent than something else.
The meeting was lengthier than I expected, lasting over two hours.
Lengthier → It is formed from "length" (from Old English "length", meaning the measurement of something from end to end) and "-ier" (a comparative suffix meaning more). The word "lengthier" means more lengthy or having greater length than something else.
Think of 'length' as the measurement from one end to another, and the '-ier' tells you it's more of that measurement. So, lengthier means having more length.
No commonly confused words.