The most common and most likely answer to this crossword clue is the 13 letter word TEMPERAMENTAL
I've seen this crossword clue in The Times
T
E
M
P
E
R
A
M
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N
T
A
L
More clues leading to the result TEMPERAMENTAL
- Difficult to handle emulsion paint gets crazed
- Unreliable name-plate term rewritten
- Unreliable way of painting people unlikely to be “detailed”
- Unreliable medium chaps follow? Not I
- Fiery oriental dish devoured by office worker and other people
- Moody freelance meant real trouble
- Paint like crazy, given to mood swings
- Last drop of emulsion in paint tin possibly having no consistency
Buddy explains!
The straight part
We know that "Unreliable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unreliable = temperamental.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 TEMPERAMENTAL mean?
TEMPERAMENTAL adjective- (notcomp) Of, related to, or caused by temperament.
- Subject to changing and unpredictable emotional states; moody, capricious; sometimes used figuratively to describe user-unfriendly or unstable machines or software that are either complicated and/or have poorly written instructions and are subsequently difficult to operate.