The term 'solemnly swear' is often used in legal contexts, such as when taking an oath or making a vow. The crossword solutions for this term are AVOW (4 letters), AVER (4 letters), IDO (3 letters), and IDOSO (5 letters). AVOW and AVER both mean to declare or affirm something firmly and sincerely. Ido is a shortened form of the phrase 'I do, ' which is commonly used in wedding ceremonies. Idoso is a combination of the words 'I do' and 'SO, ' meaning 'I do SO solemnly.'