1. Open to doubt or suspicion
   - doubtful, dubious, dubitable, in question 
2. [archaic] Inspiring fear
   - formidable, redoubtable, unnerving

See also: alarming, questionable

• Highlands
• Highlands of Scotland
• highlife
• highlight
• highlighter
• highlighting
• highly
• highly active antiretroviral therapy
• highly infective
• highly sensitive
• highly strung
• highly-developed
• highly-sexed
• highness
• highroad
• highschool
• hightail
• hightail it
• highwater
• highway
• formate
• formation
• formative
• formative cell
• formatted capacity