1. According to need (physicians use PRN in writing prescriptions)
   - as needed, as required, PRN

Encyclopedia: Pro re nata

• speaker unit
• speakerphone
• speakership
• speaking
• speaking trumpet
• speaking tube
• spear
• spear carrier
• spear thistle
• spear thrower
• spear up
• spearer
• spearfish
• spearhead
• spearhead-shaped
• spearman
• spearmint
• spearmint oil
• spearnose bat
• spearpoint
• spearwort
• spec
• special
• special act
• special agent