Verses with the word lightness in the Old Testament (2 verses):

Jeremiah 3:9
And it came to pass through the lightness of her whoredom, that she defiled the land, and committed adultery with stones and with stocks.

Jeremiah 23:32
Behold, I am against them that prophesy false dreams, saith the LORD, and do tell them, and cause my people to err by their lies, and by their lightness; yet I sent them not, nor commanded them: therefore they shall not profit this people at all, saith the LORD.