syn·kar·y·on 
(sĭn-kărē-ŏn′, -ē-ən)
(sĭn-kărē-ŏn′, -ē-ən)n.
The nucleus of a fertilized egg immediately after the male and female nuclei have fused.
[SYN- + Greek karuon, nut, seed; see kar- in the Appendix of Indo-European roots.]
syn·kar′y·onic (-ŏnĭk) adj.