Here are some possibilities for what you might have meant:
* Undermining: This word means to weaken or damage something, especially gradually.
* Example: "The constant criticism was undermining her confidence."
* Underestimating: This word means to judge something as being less important or significant than it actually is.
* Example: "He was underestimating the difficulty of the task."
* Undermentioning: This word is not a real word, but it could be used to mean mentioning something less than it deserves.
* Example: "The report undermentioned the importance of the environmental impact."
If you can provide more context or the intended meaning, I can help you find the correct word.