An old-style oath is a solemn promise or commitment to do something. The crossword solutions for this term are EGAD (4 letters), MERCY (5 letters), and PSHAW (5 letters). EGAD is an expression of surprise, dismay, or alarm. MERCY is an act of kindness, compassion, or forgiveness. PSHAW is an expression of contempt or disbelief. All three words are often used in old-style oaths to emphasize the seriousness of the commitment.