IPA: /æbˈstruːsnəs/
KK: /æbˈstrusnəs/
The quality of being difficult to understand or complex, often because it involves deep or obscure ideas.
The abstruseness of the theory made it difficult for many to understand.
Abstruseness is formed from "abstrusus" (meaning hidden or concealed) and the suffix "-ness" (meaning the state or quality of). The word refers to the quality of being difficult to understand or hidden from comprehension.
Think of something that is 'hidden' or 'concealed' — that's what 'abstruseness' means, the state of being hard to grasp.