たん単tanなるnaru
1.
Describing something that is only what it appears to be, without any additional qualities or implications; emphasizes that it is nothing more than what is stated.
2.
Indicating a condition or situation that lacks complexity or extra factors, emphasizing its straightforwardness or simplicity.
3.
Pertaining to an instance that is isolated or singular in nature, suggesting that it doesn't encompass anything beyond what is explicitly mentioned.
Example:
それは単なる偶然だと思う。