Invalidate second and third of marriages with a ring (7)
I believe the answer is:
annular
'invalidate second and third of marriages with a ring' is the definition.
I can't tell whether this defines the answer.
'invalidate second and third of marriages with a' is the wordplay.
'invalidate second' becomes 'annul' (synonyms. I am not sure about the 'second' bit.).
'and' means one lot of letters go next to another.
'third of marriages' becomes 'r' (nrd letter of 'marriages').
'with' means one lot of letters go next to another.
'r' put after 'a' is 'ar'.
'annul'+'ar' is 'ANNULAR'.
Can you help me to learn more?
(Other definitions for annular that I've seen before include "Doughnut-shaped -- a LAN run (anag)" , "Ring-shaped" , "in a band" , "Circular" , "Shaped like a ring" .)