From an unused root meaning to open (the eyes); a wink, i.e. Moment (compare pith'owm) (used only (with or without preposition) adverbially, quickly or unexpectedly) -- at an instant, suddenly, X very.
see HEBREW pith'owm
H6621. petha
מֶּתַע substantive suddenness ( √ unknown: compare Assyrian ina pitti, ina pittimma, in suddenness, instantly, DlHWB 553): — Numbers 35:22 . . . וְאִםבְּֿפֶתַע הֲדָפוֺ if he have thrust him in suddenness, before he is aware what he has done (i.e. accidentally); + מִּתְאֹם 6:9 פתאם בפתע עליו מת ימות וכי i.e. very suddenly; לְפֶתַע according to (לְ, p. 5 I 6 b) suddenness, Isaiah 29:5 פתאם לפתע והיה = at an instant, suddenly, 30:13 יבוא לפתע פתאם אשׁר שִׁבְרָהּ. As adverb accusative, suddenly, Proverbs 6:15 (= 29:1) יִשָּׁבֵר מֶּתַע, Habakkuk 2:7.