What does 常習 mean?
常習 is a Japanese noun meaning “custom; common practice; habit” in English. It is written as 常習 in kanji, じょうしゅう in hiragana, and joushuu in romaji. This word is part of JLPT N2 vocabulary.
Example sentence
シンナーなどの常習性のある物をしてると言う事は、更正する可能性が低いと思います。
I think that, as he's using addictive substances like thinner, the chance of rehabilitation is low.