Definition: The word "blunder" can be used as both a noun and a verb.
Blundering (adjective): Describing someone who frequently makes mistakes or does things clumsily.
Blunderer (noun): A person who often makes mistakes or blunders.
"To blunder into something": To accidentally get involved in a situation, often a difficult or embarrassing one.
In summary, "blunder" is a useful word to describe serious mistakes, whether in speech, writing, or actions. Remember that it often implies a lack of care or attention.