כִּסְלָהkiçlâh

in a good sense, trust; in a bad one, silliness

Pronunciation: kis-law' · Hebrew/Aramaic (Old Testament) · H3690

Meanings

1. stupidity (Psalms 85:9)

2. confidence (Job 4:6)

Same root

כֶּסֶלkeçel · H3689properly, fatness, i.e. by implication (literally) the loin (as the seat of the leaf fat) or (generally) the viscera; also (figuratively) silliness or (in a good sense) trust

Where it appears

Appears 2 times in the Bible.

Job 4:6 Doesn’t your reverence for God give you confidence? Doesn’t your life of integrity give you hope?
Psalms 85:8 I listen carefully to what God the Lord is saying, for he speaks peace to his faithful people. But let them not return to their foolish ways.

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).