Most common word for sin, about 300 times. From chata ('to miss the mark'). Remarkably, same word denotes both sin itself and sin offering atoning for it — problem and solution share one word.
Dual meaning is theologically profound. In Lev 4-5, chattath sacrifice addresses unintentional sins. Paul: God 'made him to be sin for us' (2 Cor 5:21) — Christ became sin offering.
Root ch-t-a literally 'to miss' (Judg 20:16 for slingers missing target). Sin conceived as missing God's mark. Eschatological promise: fountain opened for chattath (Zech 13:1).