KEY: Off-hand.
SYN: Impromptu, unpremeditated, extempore, unstudied,.
ANT: premeditated, studied, thought_out, elaborate.

• Insipid
• Insist
• Insnare
• Insobriety, [See SOBRIETY]
• Insolence
• Insolent
• Insoluble, [See SOLUBLE]
• Insolvable, [See INSCRUTABLE]
• Insolvent
• Inspect
• Inspector, [See INSPECT]
• Inspiration
• Inspire
• inspirit, [See ENCOURAGE]
• Inspissation
• Instability
• Install
• Instalment
• Instance
• Instant
• Instantaneous
• Instantly
• Instigate, [See URGE]
• Instil
• Instinct