御祖父さん[ojiisan] grandfather
御父さん[otossan] father
異父[ifu] same mother, different father
家父長制[kafuchousei] patriarchal authority
外祖父[gaisofu] maternal grandfather

岳父[gakufu] (man's) father-in-law
杜父魚[tofugyo] sculpin (any fish of family Cottidae, inc. the bullheads and the miller's-thumb)
義父[gifu] father-in-law
教父[kyoufu] godfather
継父[keifu] stepfather

一系[ikkei] single-family lineage
家系[kakei] family lineage
革新系[kakushinkei] liberal
共産系[kyousankei] communist controlled
銀行系カード[ginkoukeikaado] bank issued credit card

系図[keizu] family tree
系図学[keizugaku] genealogy (the study)
系統[keitou] system
系統樹[keitouju] genealogical tree