The same two dots (5)
I believe the answer is:
ditto
'the same' is the definition.
(ditto means the same as previously mentioned)
'two dots' is the wordplay.
'two dots' means two substitutions for 'dot'.
'dot' becomes 'dit' (synonyms).
'dot' becomes 'to' (I can't justify this - if you can you should give a lot more credence to this answer).
'dit'+'to'='DITTO'
Can you help me to learn more?
(Other definitions for ditto that I've seen before include "Mark used to indicate repetition" , "Two dots indicating the same again" , "Dot it for the same again" , "couple of marks" , "Copy" .)