chav is a British English word which according to the OED means "a young person of a type characterized by brash and loutish behaviour and the wearing of designer-style clothes (esp. sportswear); usually with connotations of a low social status". Of course I know it from Doctor Who. The OED tells us it's related to chavvy, an Angloromani word meaning "child", and both words are from Romani čhavo "child", related to Sanskrit शाव śāva "the young of any animal".
Monier Williams states that śāva is a form of श्वि śvi or श्वा śvā "to swell, grow, increase". Both śvi and śāva are from Proto-Indo-European *ḱeuH- "to swell; vault, hole" (IEW 592-594).
A suffixed form of *ḱeuH- became Greek κῡριος kūrios "master, lord" (from the sense "swollen, strong, powerful" (AHD)). Medieval Greek used it in phrases like κῡριακόν δῶμα kūriakon dōma "the Lord's house", and kūriakon was borrowed into West Proto-Germanic in the 4th or 5th century, becoming Old English cirice, which became church. Some of the other Germanic forms retain the /k/: Dutch kerk, Swedish kyrka, Scottish English kirk.
The OED has a long note on the etymology of church; there is some difficulty with the derivation of the Germanic word from the Greek, but it is the one generally agreed on.
The Proto-Indo-European form also became Latin cavus "hollow" as in cave and cavern.