"doku" (読) in "tsundoku" means "reading". There are several kanji that can be read as "doku". Also I think 中 (chū) from 中毒 (chūdoku, addiction) is used as a suf

"doku" (読) in "tsundoku" means "reading". There are several kanji that can be read as "doku". Also I think 中 (chū) from 中毒 (chūdoku, addiction) is used as a suffix for addiction, for example アル中 (aruchū) - alcohol addiction.