obsecration
Concise Oxford English Dictionary © 2008 Oxford University Press:
obsecration /ˌɒbsɪˈkreɪʃ(ə)n/
▶noun rare earnest pleading or supplication.
– origin ME: from L. obsecratio(n-), from obsecrare ‘entreat’, based on sacer, sacr- ‘sacred’.
'obsecration' also found in these Oxford entries:

