ˈgräd.(ˌ)ō, -ä(ˌ)tō noun
( plural grottoes also grottos )
Etymology: Italian grotta, grotto, from Latin crypta vault, cavern — more at crypt
1.
a. : a natural covered opening in the earth:
(1) : a cave typically picturesque and rocky and of limited size
(2) : a recess in a cave
(3) : a usually arched recess or hollow place (as in the side of a hill) making a natural shelter and formed by or resembling the mouth of a cave
b. : an artificial recess or structure typically arched and rocky and made to resemble a natural grotto
2. or grotto blue : a strong greenish blue that is greener and paler than cobalt blue and greener, lighter, and stronger than average cerulean blue (sense 1a) or indigo carmine