The most common and most likely answer to this crossword clue is the 4 letter word YANG
I've seen this crossword clue in The Guardian
Y
A
N
G
More clues leading to the result YANG
Buddy explains!

The straight part
We know that "Cosmic principle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cosmic principle = yang.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 YANG mean?
YANG noun- A principle in Chinese and related East Asian philosophies associated with bright, hot, masculine, etc. elements of the natural world.
- The monetary unit of Korea from 1892 to 1902, divided into 100 pun.
- The cry of the wild goose; a honk.
- To make the cry of the wild goose.