The term "unsuddenly" refers to an action or event that occurs unexpectedly or without warning. Synonyms for this word include "abruptly", suggesting a sudden change or occurrence; "instantaneously", highlighting an immediate happening; "immediately", indicating a swift action; and "unforeseen", emphasizing an event that was not anticipated. "Unexpectedly" is another suitable synonym, emphasizing the surprise element. Phrases such as "all of a sudden" or "out of the blue" can also be used to convey the idea of something happening "unsuddenly". It is important to have a broad range of synonyms for effective writing, enabling one to convey nuances and variations in meaning.