Strange coincidences in naming family members

Isn't it intriguing that French and Japanese, two totally unrelated languages, have words that can both mean father-in-law and stepfather: beau-père in French and 義父 (pronounced gifu) in Japanese? The same thing happens with belle-mère and 義母 (pronounced gibo). In those peoples' mentalities maybe the in-law or the step parent acts a substitute or additional parent and hence receives the same name. One of my Japanese dictionaries offers an interesting explanation for the meaning of 義, which reads (my translation): non-blood-related people are joined by shared children, siblings, etc.