Sordid
Etymology
From Latin "sordidus" (dirty, filthy), from "sordes" (dirt, filth). English first used it for literal dirtiness, then extended it to meanness of spirit and squalid morality. The physical grime and the moral grime have run together in the word ever since.
adjective · /SOR-did/
Morally squalid or dishonorable, often involving selfish or base motives.
What it names
The grubby underside of an affair — the greed, betrayal, or filth that people would rather keep hidden.
Example
The biography dwelt less on his triumphs than on the sordid deals that funded them.
Related idea
Seedy suggests shabby disrepute and run-down places; sordid goes further into moral squalor and self-serving motive.