Noun plymouth rock has 2 senses

• plymouth rock(n = noun.location) Array - a boulder in Plymouth supposed to be where the Pilgrims disembarked from the Mayflower; Array
is a part of plymouth
is a kind of boulder, bowlder

• plymouth rock(n = noun.animal) Array - an American breed of domestic fowl; Array
is a kind of domestic fowl, fowl, poultry