The most common and most likely answer to this crossword clue is the 8 letter word DISLOYAL
I've seen this crossword clue in The Guardian
D
I
S
L
O
Y
A
L
More clues leading to the result DISLOYAL
- I had backed ally, so shockingly traitorous
- Daily Mail ultimately so shabby, not to be trusted?
- Backstabbing ally with one “Sod off!”
- Insult the sovereign, say, when changing sides at the front like a traitor
- Roughly slay idol that’s unfaithful
- Treasonous face admitting nothing in cunning
- Only nameless lad is sadly lacking faith
- Unfaithful promiscuous lady consuming processed oils
- Untrue alloy?
- Spilt oil sadly is treacherous
Buddy explains!

The straight part
We know that "not to be trusted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not to be trusted = disloyal.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 DISLOYAL mean?
DISLOYAL adjective- Not loyal, without loyalty.