Used as a mild oath.
[Alteration of by God.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
an emphatic exclamation, regarded as a characteristic utterance of Irish people
[C19: euphemistic alteration of by God!]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
be•gor•ra(bɪˈgɔr ə, -ˈgɒr ə, bi-)
interj. Irish Eng.
(used as a euphemism for by God): It's a fine day, begorra.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.