The most common and most likely answer to this crossword clue is the 6 letter word STATER
I've seen this crossword clue in The Guardian
S
T
A
T
E
R
More clues leading to the result STATER
Buddy explains!
The straight part
We know that "This coin is ancient/I say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this coin is ancient/i say = stater.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 STATER mean?
STATER noun- A gold, silver or electrum coin of ancient Greece.
- One who states.
- A citizen of the United States of America who is a confirmed or lifelong resident of one single state.