The awful moment which follows a dorchester (q.v.) when a speaker weighs up whether to repeat an amusing remark after nobody laughed the last time. To be on the horns of an umberleigh is to wonder whether people didn't hear the remark, or whether they did hear it and just didn't think it was funny, which was why somebody coughed.
(nom commun)
pas encore traduit
revenez bientôt.
source : The Meaning of Liff