American Heritage Dictionary
(2)
Century Dictionary
(1)
GNU Webster's 1913
(1)
WordNet
(2)
Elsewhere on the web
I had planned that Grave would be a Regency effort, light and sparkling and frothy as a syllabub with just a spot of murder to spice the pot.— Magical Musings
Rhubarb syllabub, topped off with Rich chcolate truffles— Home | Mail Online
However fragrant and well-spiced, syllabub is not to be drunk by the bucketful; neither would it be satisfactory to dine off a soufflé au marasquin_, though compounded by the philanthropical Regenerator himself.— Blackwood's Edinburgh Magazine, Volume 61, No. 379, May, 1847

American Heritage Dictionary (1)
Bubble size: how much this word was used in a year
Bubble height: used more or less than expected, vs. all uses evenly distributed
You can expect to see this word about once a year.