all of a sudden

sud·den  (sdn)

adj.

1. Happening without warning; unforeseen: a sudden storm.

2. Characterized by hastiness; abrupt or rash: a sudden decision. See Synonyms at impetuous.

3. Characterized by rapidity; quick and swift.

Idiom:

all of a sudden

Very quickly and unexpectedly; suddenly.

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[Middle English sodain, from Old French, from Vulgar Latin *subitnus, from Latin subitneus, from subitus, from past participle of subre, to approach stealthily : sub-, secretly; see sub- + re, to go; see ei- in Indo-European roots.]

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sudden·ly adv.

sudden·ness n.

Thesaurus

Adv.	1.	all of a sudden - without warning; "all at once, he started shouting" all at once
	2.	all of a sudden - happening unexpectedly; "suddenly she felt a sharp pain in her side" of a sudden, suddenly