faulty

adjective2

1. •
   Having or displaying faults; not perfect; not adequate or acceptable.

   • They replaced the faulty wiring and it has worked fine ever since.
   • I don't think you can infer that from the premise. It's a faulty argument.
2. •
   (no longer used) At fault, to blame; guilty.

   • Her faultie Handmayd, which that bale did breede, / Confest, how Philemon her wrought to chaunge her weede. — 1590