Rings from Circle Line stopping District Line ultimately (7)

'rings' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.

'circle line stopping district line ultimately' is the wordplay.
'circle line' becomes 'ol' (I can't explain this - if you can you should give a lot more credence to this answer).
'stopping' means one lot of letters goes inside another (inserted letters stop or plug a gap).
'district' becomes 'area' (a district is a geographical area).
'ultimately' suggests the final letters.
The final letter of 'line' is 'e'.
'ol' put within 'area' is 'areola'.
'areola'+'e'='AREOLAE'

'from' acts as a link.

Can you help me to learn more?