errant

Short definition from Wiktionary

Adjective

1. 1
   Straying from the proper course or standard, or outside established limits.
2. 2
   Roving around; wandering.
3. 3
   Prone to err or making errors; misbehaving.
4. 4
   Obsolete form of arrant (“complete; downright, utter”).

Noun

1. 1
   A knight-errant.