Copy two dots (5)
I believe the answer is:
ditto
'copy' is the definition.
(I've seen this before)
'two dots' is the wordplay.
'two dots' can mean 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 the word above it should be repeated" , "Repeat (instruction)" , "In lists, the same again with two small marks" , "As given above" , "Repeat the word(s) above" .)