1. As a matter of instinct
   "he instinctively grabbed the knife"
   - instinctually, responsively

See also: instinctive

• underproduction
• underquote
• underrate
• underrating
• underreckoning
• underrun
• undersaturated
• underscore
• undersea
• underseal
• undersealed
• undersecretary
• undersell
• underseller
• undersexed
• undershirt
• undershoot
• undershorts
• undershot
• undershrub
• underside
• undersign
• undersize
• undersized
• underskirt