Sudden

happening, coming, made, or done quickly, without warning, or unexpectedly:
a sudden attack.
occurring without transition from the previous form, state, etc.; abrupt:
a sudden turn.
impetuous; rash.
archaic. quickly made or provided.
obsolete, .
literary. suddenly.
obsolete. an unexpected occasion or occurrence.
all of a sudden, without warning; unexpectedly; suddenly.
also, on a sudden.
contemporary examples

meanwhile, vulnerability, risk, unpredictability, and sudden transformation are the const-tutive experiences of human life.
can heritage foundation posterboy bono save the gop? james poulos march 14, 2014

obama’s strategic af-pak adviser bruce riedel unravels the plots—and what osama bin laden’s sudden spate of new messages means.
the latest al qaeda alarms bruce riedel october 2, 2010

his visit to florence was cut short by a sudden pain in his leg that prevented him from walking.
murray bernard frum, 1931–2013 david frum may 27, 2013

the sudden outbreak in fighting was unexpected for the -ssad regime, and for many residents too.
syrian refugees flee to border camps mike giglio august 5, 2012

they also spoke to “health experts” about her sudden weight gain.
lady gaga launches body revolution lizzie crocker september 24, 2012

historical examples

of a sudden it grew lighter, and the rain dwindled to a fine mist.
in the valley harold frederic

mrs. van geist fixed her niece with a sudden look of suspicion.
the spenders harry leon wilson

riley’s eyes had opened in a sudden movement of consciousness.
two thousand miles below charles willard diffin

he was not naturally bad, but he had fallen a victim to sudden temptation.
brave and bold horatio alger

but at the sight my blood rushed of a sudden through my veins and drowned my reason.
cleopatra h. rider haggard

adjective
occurring or performed quickly and without warning
marked by haste; abrupt
(rare) rash; precipitate
noun
(archaic) an abrupt occurrence or the occasion of such an occurrence (in the phrase on a sudden)
all of a sudden, without warning; unexpectedly
adverb
(mainly poetic) without warning; suddenly
adj.

late 13c., perhaps via anglo-french sodein, from old french subdain “immediate, sudden,” from vulgar latin -subit-n-s, variant of latin subitaneus “sudden,” from subitus “come or go up stealthily,” from sub “up to” + ire “come, go.” phrase all of a sudden first attested 1680s, earlier of a sudayn (1590s), upon the soden (1550s). sudden death, tie-breakers in sports, first recorded 1927; earlier in reference to coin tosses (1834).
see: all of a sudden