icebreaker

noun

1. Nautical. a ship specially built for breaking navigable passages through ice.
2. an opening remark, action, etc., designed to ease tension or relieve formality: A mild joke can be a good icebreaker.
3. a tool or machine for chopping ice into small pieces.

noun

1. Also called: iceboat a vessel with a reinforced bow for breaking up the ice in bodies of water to keep channels open for navigation
2. any tool or device for breaking ice into smaller pieces
3. something intended to relieve mutual shyness at a gathering of strangers