The most common and most likely answer to this crossword clue is the 7 letter word VARIANT
I've seen this crossword clue in Financial Times
V
A
R
I
A
N
T
Buddy explains!

The straight part
We know that "It’s unusual" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s unusual = variant.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 VARIANT mean?
VARIANT noun- Something that is slightly different from a type or norm.
- A different sequence of a gene (locus).
- A variable that can hold any of various unrelated data types.
- One of a set of words or other linguistic forms that conveys the same meaning or serves the same function.
- Showing variety, diverse.
- Showing deviation or disagreement.
- Variable.
- Covariant and/or contravariant.