1) General subject: against (contrary to) expectation, all at once, all of a heap, all of a sudden, by surprise, overnight, short, snap, sudden, suddenly, unaware, unawares, abruptly
2) Engineering: unexpectedly
3) Abbreviation: (All Of A Sudden) AOAS
4) Jargon: smack
5) Makarov: at unawares, out of the blue
6) Phraseological unit: out of left field
Универсальный русско-английский словарь. Академик.ру. 2011.