unprincipled (adj.)

• conscienceless
• corrupt
• corrupted
• criminal
• crooked
• dark
• devious
• dishonest
• dishonorable
• dissolute
• doubtful
• dubious
• evasive
• felonious
• fishy
• fraudulent
• ill-gotten
• immoral
• indirect
• insidious
• licentious
• mercenary
• profligate
• questionable
• reprobate
• rotten
• shady
• shameless
• shifty
• sinister
• slippery
• suspicious
• tricky
• unconscientious
• unconscionable
• underhand
• underhanded
• unethical
• unsavory
• unscrupulous
• venal