1. Depost of lime, usually from hard water on pipes, kettles, etc. 
2. Lime deposited from hard water
   "pipes can even become completely blocked with limescale deposits over the course of time"

Encyclopedia: Limescale

• American mastodon
• American mastodont
• American merganser
• American mink
• American mistletoe
• American mountain ash
• American oil palm
• American olive
• American organ
• American oriole
• American parasol
• American parsley fern
• American Party
• American pasqueflower
• American pennyroyal
• American persimmon
• American pit bull terrier
• American plaice
• American plan
• American plane
• American pulsatilla
• American quaking aspen
• American raspberry
• American rattlebox
• American red elder