- lacking or not based on moral scruples or principles: an unprincipled person; unprincipled behavior.
- not instructed in the principles of something (usually followed by in).
- lacking moral principles; unscrupulous
- (foll by in) archaic not versed in the principles of (a subject)
adj.1630s, “not instructed” (in something), from un- (1) “not” + principled. Meaning “not honorable” is recorded from 1640s.