1. Without warning
   - all at once 
2. Happening unexpectedly
   - suddenly, of a sudden

Encyclopedia: All of a sudden

• Haemosporidia
• haemosporidian
• haemostasia
• haemostasis
• haemostat
• haemostatic
• haemothorax
• Haemulidae
• Haemulon
• Haemulon album
• Haemulon aurolineatum
• Haemulon macrostomum
• Haemulon malanurum
• Haemulon parra
• hafiz
• hafnium
• haft
• Haftarah
• Haftorah
• hag
• Hagada
• Haganah
• hagberry
• hagberry tree
• hagbut