Solution

DIFFICULTY

3 clues

Obstacle

Word class: Common noun
Nature of clue: Synonym
Difficulty: Easy

Other solutions to Obstacle

Problem

Word class: Common noun
Nature of clue: Synonym
Difficulty: Very easy

Other solutions to Problem

Trouble

Word class: Common noun
Nature of clue: Synonym
Difficulty: Easy

Other solutions to Trouble

AIL

Words are categorized by artificial intelligence: there can be mistakes.