פִּתְאוֹםpithʼôwm

suddenness, usually as adverb accusative suddenly (Psalms 64:8; Numbers 12:4; Joshua 10:9; Joshua 11:7; Isaiah 47:11)

Pronunciation: pith-ome' · Hebrew/Aramaic (Old Testament) · H6597

Same root

פֶּתַעpethaʻ · H6621a wink, i.e. moment(used only (with or without preposition) adverbially, quickly or unexpectedly

Where it appears

Appears 25 times in the Bible.

Numbers 6:9 “If someone falls dead beside them, the hair they have dedicated will be defiled. They must wait for seven days and then shave their heads. Then they will be cleansed from their defilement.
Numbers 12:4 So immediately the Lord called to Moses, Aaron, and Miriam and said, “Go out to the Tabernacle, all three of you!” So the three of them went to the Tabernacle.
Joshua 10:9 Joshua traveled all night from Gilgal and took the Amorite armies by surprise.
Joshua 11:7 So Joshua and all his fighting men traveled to the water near Merom and attacked suddenly.
2 Chronicles 29:36 And Hezekiah and all the people rejoiced because of what God had done for the people, for everything had been accomplished so quickly.
Job 5:3 I have seen that fools may be successful for the moment, but then comes sudden disaster.

See every passage

Numbers 6:9, 12:4
Joshua 10:9, 11:7
2 Chronicles 29:36
Job 5:3, 9:23, 22:10
Psalms 64:4, 64:7
Proverbs 3:25, 6:15, 7:22, 24:22
Ecclesiastes 9:12
Isaiah 29:5, 30:13, 47:11, 48:3
Jeremiah 4:20, 6:26, 15:8, 18:22, 51:8
Malachi 3:1

Source: Brown, Driver and Briggs, Hebrew and English Lexicon of the Old Testament (1906), public domain; markup by unfoldingWord, CC BY (github.com/unfoldingWord/Brown-Driver-Briggs-Enhanced).