The most common and most likely answer to this crossword clue is the 3 letter word JAY
I've seen this crossword clue in Financial Times
J
A
Y
Buddy explains!
The straight part
We know that "One tweets/t/h/e tenth character" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one tweets/t/h/e tenth character = jay.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does JAY mean?
JAY noun- Any one of the numerous species of birds belonging to several genera within the family Corvidae, including Garrulus, Cyanocitta, Aphelocoma, Perisoreus, Cyanocorax, Gymnorhinus, Cyanolyca, Ptilostomus, and Calocitta, allied to the crows, but smaller, more graceful in form, often handsomely coloured, usually having a crest, and often noisy.
- Other birds of similar appearance and behaviour.
- Any of various large papilionid butterflies of the genus Graphium.
- A dull or ignorant person. It survives today in the term jaywalking.
- Promiscuous woman; prostitute.
- The name of the Latin-script letter J.
- A marijuana cigarette; a joint.