Dublin landlord appears after a period in America (7,6)
I believe the answer is:
capital letter
'a period in america' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'dublin landlord appears' is the wordplay.
'dublin' becomes 'capital' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'landlord' becomes 'letter' (landlords let property).
'appears' means one lot of letters go next to another (some letters appear after others).
'capital'+'letter'='CAPITAL LETTER'
'after' acts as a link.
Can you help me to learn more?
(Other definitions for capital letter that I've seen before include "Beginning of sentence" , "I, for example" , "Sentences start with one" , "I may be" .)