rul ‧ er /ˈruːlə $ -ər/ BrE AmE noun [countable]
[ Word Family: noun : ↑ rule , ↑ ruler , ↑ ruling , ↑ unruliness ; adjective : ↑ ruling , ↑ unruly , ↑ ruled ; verb : ↑ rule , ↑ overrule ]
1 . someone such as a king or queen who has official power over a country or area
2 .
a long flat straight piece of plastic, metal, or wood that you use for measuring things or drawing straight lines:
a 12-inch ruler