Rings from Circle Line stopping District Line ultimately (7)

'rings' is the definition.
Although both the answer and definition are plural nouns, I don't understand how one could define the other.

'circle line stopping district line ultimately' is the wordplay.
'circle line' becomes 'ol' (I can't explain this - if you can you should believe this answer much more).
'stopping' indicates putting letters inside (stopping can mean blocking a gap).
'district' becomes 'area' (a district is a geographical area).
'ultimately' indicates one should take the final letters.
The last letter of 'line' is 'e'.
'ol' put within 'area' is 'areola'.
'areola'+'e'='AREOLAE'

'from' is the link.

Can you help me to learn more?