Proto-Indo-European Roots

Root/Stem: *swek'ur- / *swek'ru'-

Meanings: husband's father / mother

Cognates (18):

Hellenic Greek hekuros (husband's father)

Italic Latin socer (husband's father), socrus (husband's mother)

Celtic Welsh chwegr (husband's mother), Cornish hweger

Indic Sanskrit çvaçura- (husband's father)

Dardic & Nuristani

Iranian Avestan xvasura- (husband's father)

Anatolian

Tocharian

Armenian Armenian skesur (husband's mother), skesrair (husband's father)

Balkan Albanian vjehe"r, vjer (husband's father)

Germanic Common Germanic *swixaraz, >
Gothic swaihra (husband's father), swaihro (husband's mother), Old High German swehur (husband's father), Old English swéor (husband's father), sweger (husband's mother), Old Icelandic swæra (husband's mother);
German Schwiegervater, Schwiegermutter

Baltic Lithuanian šešuras (husband's father)

Slavic Common Slavic *svekürü (husband's father), *svekry (husband's mother); >
Russian svekor (husband's father), svekrov' (husband's mother)

Notes: The Proto-Indo-European language, like a lot of ancient languages, had different words for dozens of family relatives. Later, when languages of the fasmily started turning into analytic ones, those relative terms changed into neutral and abstract words like 'father-in-law', 'brother-in-law', 'grandfather' etc.
Archaic Indo-European languages still preserve distinction between the words 'husband's father' and 'wife's father': for example, Russian svekor and test', which have nothing in common etyomologically and derive from completely different stems.
The word is very ancient, it usually belonged to o-stems, and its feminine counterpart - to ú-stems (like in Slavic, Italic, Armenian).

*Root/Stem:*	swek'ur- / swek'ru'-

*Meanings:*	husband's father / mother

*Cognates (18):*
Hellenic	Greek *hekuros* (husband's father)
Italic	Latin *socer* (husband's father), *socrus* (husband's mother)
Celtic	Welsh *chwegr* (husband's mother), Cornish *hweger*
Indic	Sanskrit *çvaçura-* (husband's father)
Dardic & Nuristani
Iranian	Avestan *xvasura-* (husband's father)
Anatolian
Tocharian
Armenian	Armenian *skesur* (husband's mother), *skesrair* (husband's father)
Balkan	Albanian *vjehe"r, vjer* (husband's father)
Germanic	Common Germanic swixaraz, > Gothic swaihra* (husband's father), *swaihro* (husband's mother), Old High German *swehur* (husband's father), Old English *swéor* (husband's father), *sweger* (husband's mother), Old Icelandic *swæra* (husband's mother); German *Schwiegervater, Schwiegermutter*
Baltic	Lithuanian *šešuras* (husband's father)
Slavic	Common Slavic svekürü (husband's father), svekry (husband's mother); > Russian *svekor* (husband's father), *svekrov'* (husband's mother)

Notes:	The Proto-Indo-European language, like a lot of ancient languages, had different words for dozens of family relatives. Later, when languages of the fasmily started turning into analytic ones, those relative terms changed into neutral and abstract words like 'father-in-law', 'brother-in-law', 'grandfather' etc. Archaic Indo-European languages still preserve distinction between the words 'husband's father' and 'wife's father': for example, Russian *svekor* and *test'*, which have nothing in common etyomologically and derive from completely different stems. The word is very ancient, it usually belonged to o-stems, and its feminine counterpart - to ú-stems (like in Slavic, Italic, Armenian).