Arrant

1. Utter; complete (with a negative sense).
2. Obsolete form of errant.

Usage notes

Particularly used in the phrase “arrant knaves”, quoting Hamlet, and “arrant nonsense”.^[3]

Some dictionaries consider arrant simply an alternative form of errant, but in usage they have long since split.

The word has long been considered archaic, may be confused with errant, and is used primarily in clichés, on which basis some recommend against using it.