5 Answers

at·oll   [at-awl, -ol, -ohl, uh-tawl, uh-tol, uh-tohl] 
noun
a ring-shaped coral reef or a string of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon.
Origin:
1615–25; earlier atollon < French: a word used in early descriptions of the Maldive Island atolls; said to be Divehi (Indo-Aryan language of the Maldives) ato?u

An island that encircles a lagoon (fully encircles or almost full encircles).  Made by coral reefs.

its a bit like,when you lose all your money,{I have nothing Atoll,}

at·oll [at-awl, -ol, -ohl, uh-tawl, uh-tol, uh-tohl] 
noun
a ring-shaped coral reef or a string of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon.

Origin: 
1615–25;  earlier atollon  < French:  a word used in early descriptionsof the Maldive Island atolls; said to be Divehi (Indo-Aryan language ofthe Maldives) ato?u