WordNet (r) 3.0 (2006):

pater
    n 1: an informal use of the Latin word for father; sometimes
         used by British schoolboys or used facetiously

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "pater":
   abba, dad, daddy, father, foster father, genitor, governor, old,
   pa, pap, papa, pappy, paterfamilias, patriarch, pop, pops, sire,
   stepfather, the old man



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PATER. Father. A term used in making genealogical tables.