The Avestan word napāt-
Word napāt-
Meaning grandson
See also Proto-Indo-European: *népōts ‘grandson, nephew’
Latin: nepōs ‘grandson, nephew’
Sanskrit: nápāt- ‘descendant, offspring, grandson’

Other words that might be of interest
hunu-š ‘son’, nar- ‘man’, nāirī ‘woman’, mašiia- ‘mortal, man’, vīra- ‘man’, amərətatāt- ‘immortality’