1. Not required by rule or law
   - nonobligatory

See also: optional

• slowpoke
• slowworm
• SLR
• SLS
• slub
• slubbed
• slubber
• slubberdegullion
• sludge
• sludgy
• slue
• slug
• slugabed
• slugfest
• sluggard
• slugger
• sluggish
• sluggishly
• sluggishness
• sluice
• sluice down
• sluice valve
• sluicegate
• sluiceway
• sluicing