The most common and most likely answer to this crossword clue is the 11 letter word ODD-LOOKING
I've seen this crossword clue in The Times
O
D
D
-
L
O
O
K
I
N
G
Buddy explains!
The straight part
We know that "Strange to witness" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case strange to witness = odd-looking.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.