Briary

Covered with or full of briars; thorny, prickly, and difficult to pass through; also used figuratively to mean difficult or complicated.

From 'briar' (a prickly plant from Old English 'brēr') combined with the adjective suffix '-y,' creating 'briery,' which evolved into the spelling 'briary.' The suffix '-y' means 'full of' or 'characterized by.'