I’ve always thought of an ancestor as someone from whom you are directly descended – who is dead. When your grandparents die, they become ancestors. But if you have great grandparents living or even g-g grandparents living (it does happen), they are not considered your ancestors while still alive.
Not really.
Well, then, obviously, I stand corrected.
NM, misunderstood the OP.
I repeat: That’s just me.
Lots of nitpickery going on here.
Direct ancestors are those people who parented you or those who gave rise to you by parenting, in a direct line – strting with your parents, your grandparents, your great-grandparents, and so on back. It is usually not used to refer specifically to parents or grandparents, implying a greater range of descent than ‘second order’ (to use Chronos’s mathematical analogy).
Collateral ancestors are those from whom you are not directly descended, but who were in some way significant and who were in close degrees of consanguinity to direct ancestors. If some Governor of New Mexico was your great-great-grandmother’s cousin and you wish to claim kinship to him, he’s a collateral ancestor. I’d hesitate to put specific bounds on this, but the usage seems limited to at maximum half-first-cousins by marriage – your great-grandmother’s sister was the second wife of a man whose daughter by his first wife (whom she helped raise) married someone famous, who becomes a collateral ancestor at the extreme use of the claim. Nearly always, ‘collateral ancestor’ means someone with some degree of historifcal importance who is not in your direct line of ancestry but a member of whose extended family is.
Seems clear enough to me.