The most common and most likely answer to this crossword clue is the 7 letter word DRACHMS
I've seen this crossword clue in The Guardian
D
R
A
C
H
M
S
Buddy explains!

The straight part
We know that "coins of antiquity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coins of antiquity = drachms.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 DRACHMS mean?
DRACHMS noun- A small unit of weight, variously:
- The currency of Greece in ancient times and again from 1832 until 2001, with the symbol ₯, since replaced by the euro.
- A coin worth one drachma.
- An Ancient Greek weight of about 66.5 grains, or 4.3 grams.
- A later Greek weight equal to a gram.