The most common and most likely answer to this crossword clue is the 8 letter word MOREOVER
I've seen this crossword clue in The Daily Telegraph
M
O
R
E
O
V
E
R
More clues leading to the result MOREOVER
- Second traveller swallows tablet on top of that
- Besides, Rome's destroyed and finished
- Doctor, traveller around east also
- Rome collapsed in excess, may I add
- Further extra to the other side
- Order twisted vagrant to keep distance, finally further
- Flash car saving energy as well
- Flash traveller touring Spain as well
- Person changing position about product of mine, in addition
- Extra extra in addition
Buddy explains!

The straight part
We know that "in addition" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in addition = moreover.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 MOREOVER mean?
MOREOVER adverb- In addition to what has been said; furthermore; additionally.