The most common and most likely answer to this crossword clue is the 5 letter word OGHAM
O
G
H
A
M
More clues leading to the result OGHAM
- Turn back actor’s script
- Old characters journey back to meet flood survivor
- Old characters making comeback exit play without permit
- Type of writing produced by old German thespian
- Initially, old German half as mysterious as ancient writing system
- Van Gogh amazingly conceals an ancient Celtic alphabet
- Old hag damaged front of monument showing an ancient alphabet
- Old-fashioned characters try rolls with meat
- Ancient characters blunder when defending luvvie
Buddy explains!

The straight part
We know that "an ancient alphabet" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an ancient alphabet = ogham.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 OGHAM mean?
OGHAM noun- A single character in this alphabet.
- An ancient Celtic alphabet historically used to write Primitive Irish.