WordWeb Online

1. The quality of being covered with prickly thorns or spines
   - prickliness, bristliness, spininess
    
2. A rough and bitter manner
   - bitterness, acrimony, acerbity, jaundice, tartness
    
3. The property of being full of difficulties, complexities, or controversial points.
   "And, given the thorniness of the issues on the table, a work stoppage at all West Coast ports is not to be ruled out."

Type of: difficultness, difficulty, disagreeableness, fix [informal], hole [informal], jam [informal], kettle of fish [informal], mess [informal], muddle [informal], pickle [informal], raggedness, roughness