窃盗 (せっとう) uses the on'yomi 窃 (セツ), meaning to steal, and 盗 (トウ), also meaning to steal. The small っ (sokuon) is crucial here. The wrong reading せつとう misses this sokuon, changing the pronunciation. せつだ and せつぼう are misreadings of 盗. It refers to the crime of taking someone else's property without permission, i.e., theft or stealing.

窃盗（せっとう）は両漢字とも音読み。窃（セツ）も盗（トウ）も「ぬすむ」の意味。促音「っ」を含むのが正しい読みで、せつとうは促音を欠く誤り。せつだ・せつぼうは盗の誤読です。他人の財物をひそかに盗む犯罪行為を指します。