This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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

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

adj. Characterized by rapidity; quick and swift.

idiom. all of a sudden Very quickly and unexpectedly; suddenly.

adj. Happening quickly and with little or no warning, snell.

ad. Suddenly.

n. An unexpected occurrence; a surprise.

adj. Happening without previous notice or with very brief notice; coming unexpectedly, or without the common preparation; immediate; instant; speedy.

adj. Hastly prepared or employed; quick; rapid.

adj. Hasty; violent; rash; precipitate.

ad. Suddenly; unexpectedly.

n. An unexpected occurrence; a surprise.

Happening without notice, instantly and unexpectedly; immediate; instant.

Found or hit upon unexpectedly.

Hastily made, put in use, employed, prepared, etc.; quick; rapid.

Hasty; violent; rash; precipitate; passionate.

In zoology, abrupt; sharply defined from neighboring parts: as, a sudden antennal club; a sudden truncation.

n. That which is sudden; a surprise; an unexpected occurrence.

Suddenly; unexpectedly.

adj. happening without warning or in a short space of time

"The term sudden infant death syndrome (Sids) was introduced in 1969 as a recognised category of natural death that carried no implication of blame for bereaved parents."

choppy    fulminant    sharp    explosive    emergent    jerky    abrupt   

gradual    unsudden   

abrupt    on such a sudden    upon all suddens    all of (on) a sudden   

suddenly    suddenwoven    suddenness    sudden death    all of a sudden   

unexpected    unusual    abrupt    unlooked-for    immediate    instant    speedy    quick    rapid    hasty   

unexpected    quick    slight    intense    abrupt