The most common and most likely answer to this crossword clue is the 11 letter word PREHISTORIC
I've seen this crossword clue in The Times
P
R
E
H
I
S
T
O
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I
C
More clues leading to the result PREHISTORIC
Buddy explains!
The straight part
We know that "Ancient" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ancient = prehistoric.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 PREHISTORIC mean?
PREHISTORIC adjective- Having lasted from a remote period; having been of long duration; of great age, very old.
- Existent or occurring in time long past, usually in remote ages; belonging to or associated with antiquity; old, as opposed to modern.
- (history) Relating to antiquity as a primarily European historical period; the time before the Middle Ages.
- Experienced; versed.
- Former; sometime.
- (properly) Of or relating to the epoch before written record.