1. Happening without warning; unforeseen: a sudden storm.
2. Happening or done without delay; hasty or immediate: a sudden decision.
3. Characterized by sharp change in elevation; precipitous: a sudden drop in the ocean floor.
all of a sudden
Very quickly and unexpectedly; suddenly.
[Middle English sodain, from Old French, from Vulgar Latin *subitānus, from Latin subitāneus, from subitus, from past participle of subīre, to approach stealthily : sub-, secretly; see SUB- + īre, to go; see ei- in the Appendix of Indo-European roots.]
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