"Unduer" is not a commonly used word, making it difficult to find exact synonyms. However, depending on the context, there are several words that could be used interchangeably. For example, instead of "unduer", words like "changeable", "wavering", "unstable", "inconsistent", or "fluctuating" could be used to describe something that is not steady or regular. Alternatively, the word "undo" could be used to mean to "reverse" or "erase", which could be an appropriate synonym depending on the context in which "unduer" is being used. Ultimately, the appropriate synonym for "unduer" will depend on how it is being used and the specific meaning that is intended.