Hold one picture and every use of this word falls into place: two things born of the same parent. Latin cognatus means born together, and that is exactly what the word still does — it puts two items on one family tree and says they came down from the same source. Change what sits on the tree and you get each of the senses: put people on it and you get blood relatives; put words on it and you get English house beside German Haus; put subjects on it and you get history beside archaeology. The word never measures how alike two things look now. It only says where they came from.
From the word’s history
Borrowed from Latin cognatus, related by blood, from co- (together) plus gnatus (born). A doublet of connate.
借自拉丁文 cognātus（有血緣的），由 co-（一起）加 gnātus（出生的）組成，字面就是「一起出生」。英文 connate 是它的同源雙生字。
Wiktionary, "cognate"
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