unresponsible
/(ˌ)ʌnrɪˈspɒnsɪbl/adjective
1Not responsible or accountable to any other person or thing; unaccountable.
- Apparently rare before late 18th cent..
2Originally: that cannot be relied on; unreliable. Later more usually: reckless, imprudent, irresponsible.
Origin
Early 17th century (in an earlier sense). From un- + responsible. Compare earlier unresponsable.