MEANING: adjective:
1. Traveling, especially in search of adventure.
2. Erring, straying, or moving aimlessly.

ETYMOLOGY: For 1: From Old French errer (to travel), from Latin iterare (to travel), from iter (road, trip).
For 2: From Old French errer (to err), from Latin errare (to wander or to err).
Earliest documented use: 1400s.

NOTES: How in the world can a word have so many different meanings? Blame homographs, two different words having the same spelling (lead, the verb & lead, the metal). In the case of today’s word, two Latin words (iterare and errare) evolved into the Old French errer. This homographic confusion continued when the words traveled to English. As if this weren’t enough, the word errant has morphed into another word resulting in further confusion: arrant.
Only the first adjective form is used postpositively.

TERRANT - Earthlike

E.R. RANT - there's a madman yelling and screaming in the Emergency Room!

'ERRANG - what you caught yesterday when you were fishing (past tense of 'ERRING)