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

Encyclopedia: All of a sudden

• razor-fish
• razor-sharp
• razorback
• razorback hog
• razorbacked hog
• razorbill
• razorblade
• razz
• razzamatazz
• razzing
• razzle
• striped mullet
• striped racer
• striped skunk
• striped squirrel
• striped violet
• striper
• stripes
• stripey
• striping
• stripling
• stripped
• stripped-down
• stripper
• stripper well