1. Causing fear or dread or terror
   "horrendous explosions shook the city"
   - awful, dire, direful, dread, dreaded, dreadful, fearful, fearsome, frightening, horrific, terrible

See also: alarming

• unpractical
• unpracticed
• unpractised
• unprecedented
• unprecedentedly
• unpredictability
• unpredictable
• unpredictably
• unpredicted
• unpredictive
• unprejudiced
• unpremeditated
• unprepared
• unprepossessing
• unpresentable
• unpresidential
• unpressed
• unpretending
• unpretentious
• unpretentiously
• unpretentiousness
• unpreventable
• unpriestly
• unprincipled
• unprintable