Archaism is the deliberate use of words, spellings, grammar, or turns of phrase that sound old-fashioned or belong to an earlier stage of the language. Poets may use archaic language to create a historical setting, a formal tone, or a sense of distance, reverence, or tradition.
Common examples include words such as thee, thou, and hath, but archaism can also appear in older sentence patterns or spellings.
Example
O gentle moon, thou keepest watch above
and dost not sleep while all the gardens dream.