seedy underbelly

「内定」に関するthe Japan Timesの記事からの引用です。seedyはもともと「種（たね）の多い[ある]」という意味の形容詞ですが，そこから転じて「いかがわしい」という意味があります（『プログレッシブ英和中辞典』小学館）。
さらにunderbellyは過去にブログでも採り上げられていますが，今回は「(社会などの)恥部」という意味（『プログレッシブ英和中辞典』同上）。このunderbellyは「下(腹)部」を意味し，そこから「弱点」，さらに上記の意味を持つようになったようです。以上からseedy underbellyは「いかがわしい社会の暗部」と解釈できます。（Koyamamoto）

cf. http://d.hatena.ne.jp/A30/20120127/1327651541

Would-be NTV announcer’s fate hangs on issues of morality and fraud
The prevalence of the employment custom of saiyō naitei (tentative job offers) may well be peculiar to Japan. As I touched upon in my March 27, 2012, column, university juniors and seniors skip class to attend work seminars, company orientations, internships and, finally, a series of tests and interviews with prospective employers.
… In Japan, working as a hostess is a mizushōbai job. Mizushōbai literally means the “water trade” but refers to the industry that revolves around liquor, and is seen by some to be society’s seedy underbelly. NTV believed her past employment as a hostess could tarnish the reputation of the station, and so it just wouldn’t do to have her as a news announcer.
http://www.japantimes.co.jp/community/2014/11/26/issues/ntv-announcers-fate-hangs-issues-morality-fraud/#.VHXcV77EPFY