unprincipled

adjective

1. lacking or not based on moral scruples or principles: an unprincipled person; unprincipled behavior.
2. not instructed in the principles of something (usually followed by in).

adjective

1. lacking moral principles; unscrupulous
2. (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.