Terminology
The English term king is derived from the Anglo-Saxon cyning, which in turn is derived from the Common Germanic *kuningaz. The Common Germanic term was borrowed into Finnish and Estonian at an early time, surviving in these languages as kuningas.
The term is notably different from the word for "king" in other Indo-European languages (*rēks "ruler"; Latin rēx, Sanskrit rājan and Irish ríg). It is a derivation from the term *kunjom "kin" (Old English cynn) by the -inga- suffix. The literal meaning is that of a "scion of the kin", or perhaps "son or descendant of one of noble birth" (OED).
There were other terms for the Germanic king in early Germanic languages, derived from the word for "the people, the nation" rather than "kin". These are Old Norse fylkir (from *fulka) and Gothic þiudans (from *þeuda).
Comparable terms did not necessarily refer to a king but to any member of the nobility, e.g. Old English dryhten (from *druhtiz "army, folk, people"), þēoden (from *þeuda) and æðeling (from *aþel "noble family").
In Germanic poetry, kennings in use for "king" or "lord" include Old English beah-gifa "giver of rings" (Beowulf).
Earl/jarl was a title for a chieftain or leader of a small force of men below the level of kingship. The English lord (hlāford) is another kenning for a chieftain, without parallels in other Germanic languages. Old Norse hofðing (Modern German Häuptling) was a term for "chieftain", literally "head man". The Latinate captain introduced in the late medieval period has the same meaning.
Read more about this topic: Germanic Kingship