An afterthought to tweet and text (10)
I believe the answer is:
postscript
'an afterthought' is the definition.
(a PS in a letter)
'tweet and text' is the wordplay.
'tweet' becomes 'post' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' means one lot of letters go next to another.
'text' becomes 'script' (I've seen this before).
'post'+'script'='POSTSCRIPT'
'to' is the link.
Can you help me to learn more?
(Other definitions for postscript that I've seen before include "belated comment" , "part of letter" , "Last added words" , "Afterthought to a letter" , "Addition to a letter" .)