Somewhat difficult or hard to understand; a bit troublesome or pedantic (often used about explanations, writing, or speech).
この教科書は専門用語が多くて小難しい。
This textbook is full of technical terms and a bit hard to follow.
説明が小難しくて、初心者にはわかりにくいと思う。
The explanation is somewhat difficult, so I think beginners will find it hard to understand.
彼は議論になると小難しい話をして場を重くすることがある。
When discussions start he sometimes talks pedantically, which can make the atmosphere heavy.