Self-referential (so far) term for the linguistic idiosyncracies restricted to a family or household (Greek oikos, hearth) and passed on down the generations, often resulting from obscure original references now lost. Snappy responses to stupid questions or irritating banal comments seem to be the most fruitful source. Thus, in an arbitrary sample household the comment "it's hot" uttered at the dinner table (for those old enough to remember dinner tables) always elicits one of "It's been in a hot place" or "It's supposed to be a merit" (families do, of course, tend to merge two (or more) separate sets of oikolect from the parents' families, and more complex family structures widen it still further; in this case neither alternative has as yet gained dominance; however "riding up and down the Maidstone road on a bicycle" in answer to "what are you doing" encountered no competing form from the other side of the family).
Other sources include baby talk and childhood malapropisms - although these die out fast during the "embarrassing parent of teenagers" phase - and (mis)quoted fragments of once-favoured but now forgotten poems and prose ("It is quite simple if you have any strength in your thumbs" on carrying out any task which someone else has failed to do, or "Out into the night, starless and bible black, down to the slow, black, sloe-black crow-black fishing-boat bobbing sea" as a response to "Where are you going?")