The term 'archaic verb' refers to verbs that are no longer used in modern language. The two crossword solutions for this term are 'HAST' and 'DOEST', both of which are four and five letter words respectively. HAST is an old-fashioned form of the verb 'HAVE' and DOEST is an old-fashioned form of the verb 'DO'. Both of these verbs were commonly used in English language prior to the 19th century, but HAVE since become obsolete.