Strong's H3689כֶּסֶל: properly, 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 KJV:confidence, flank, folly, hope, loin.
Meanings: Brown-Driver-Briggs (1906) and Strong's Hebrew Dictionary (1890), public domain, via the Open Scriptures Hebrew Bible Project (CC BY 4.0). TWOT numbers for reference only.
Root family 1011: כָּסַלkāsal — be, become stupid; be fat, silly; be foolish