1. A word, phrase, or usage that is no longer in common use; an obsolete or old-fashioned expression
The word 'thee' is an archaism in modern English.
A palavra 'vós' é um arcaísmo no português moderno.
2. The use or imitation of archaic language or style
The author's archaism in the novel gives it a classical feel.
O arcaísmo do autor no romance lhe confere um ar clássico.