The most common and most likely answer to this crossword clue is the 4 letter word YLEM
Y
L
E
M
Buddy explains!
The straight part
We know that "supposedly original material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case supposedly original material = ylem.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 YLEM mean?
YLEM noun- In the Big Bang theory, the hot and dense plasma which made up the cosmos at the time of recombination in an early stage of its expansion and cooling, when the first atoms formed and photons decoupled. The ylem is regarded as the source of the cosmic microwave background.