Possible Clues:

• When repeated twice, et cetera
• When tripled, ''et cetera''
• One-third of a verbal ellipsis
• Third of a Seinfeld line
• When repeated twice, "and so on"
• When said three times, 'and so on'
• Part of a 'Seinfeld' catchphrase
• When repeated, "Blah, blah, blah" kin
• When repeated twice, "et cetera"
• 'Et cetera,' when tripled