The most common way to say “difficult” in Spanish is:

  • difícil

Examples:

  • “This exam is difficult” → “Este examen es difícil.”
  • “A difficult question” → “Una pregunta difícil.”

Other words you might see depending on context are complicado (complicated) or duro (hard/tough), but if you just want a straightforward translation of “difficult,” use difícil.