Related Clues:

• Talked a blue streak?
• Promised emphatically
• Made an oath
• Pledged
• Crossed one's heart, e.g.
• Used four-letter words
• Attested
• Gave earnest assurances
• Gave one's word
• Gave testimony
• Insisted absolutely
• Used colorful language
• Promised
• Insisted
• Blasphemed