The most common and most likely answer to this crossword clue is the 8 plus 10 letter word MAVERICK (MATERIAL)
I've seen this crossword clue in The Guardian
M
A
V
E
R
I
C
K
(
M
A
T
E
R
I
A
L
)
Buddy explains!
The straight part
We know that "Unorthodox" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unorthodox = maverick (material).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.