IPA: /æbˈstruːsli/
KK: /æb'stru:sli/
In a way that is difficult to understand or comprehend.
The professor explained the theory abstrusely, leaving many students confused.
Abstrusely → It is formed from "abstrusus" (from Latin, meaning hidden or concealed) and the adverbial suffix "-ly" (meaning in a manner). The word "abstrusely" means in a manner that is difficult to understand or hidden from comprehension.
Think of something that is 'hidden' or 'concealed' — that's what 'abstrusely' means, describing a way of being difficult to grasp.
No commonly confused words.