having or covered with protective barbs or quills or spines or thorns or setae etc ; "a horse with a short bristly mane"; "bristly shrubs"; "burred fruits"; "setaceous whiskers"
Like a thorn or thorns; hence, figuratively, troublesome; vexatious; harassing; perplexing
If you describe a problem as thorny, you mean that it is very complicated and difficult to solve, and that people are often unwilling to discuss it. the thorny issue of immigration policy