What does 'sake' actually mean?

[Desiderata]

My three year old asked me this today, out of the blue .. as they do.

I expect he overheard me saying 'Oh, for heaven's sake' or something equally Joyce Grenfellesque when I placed my naked foot squarely on a small, green building block this afternoon. I mean, he didn't ask me what FUCK meant, so I must have alluded to the heavens, right?

Any hooo, without resorting to the dictionary or to Google, can anyone explain to me what 'sake' means ... as in, 'for heaven's sake', or 'we should go to the party for Mary's sake.'

Ok, I'm off to bed now for "my sake"
Night all.

He's clever alright, Mhamai. My only hope for him is that he doesn't go to Uni.

I'd hate to have it knocked out of him

Good night, gorgeous.

God I know the feeling! Mwah, night my lovely.

Who is Pete?

Dependent Clause.

A dependent clause, eh? Clever arse

Isn't a dependent clause different? It's just another term for 'subordinate clause', surely? So in a sentence such as:

If you don't know the answer, you must be stupid'

'you must be stupid' is the main clause and 'If you don't know the answer' is the dependent clause.

This is surely just a strong collocation of 'goodness'' or 'heaven's' and 'sake' to create an idiomatic expression.

As for Pete, I wonder if it is a corruption of 'pity'?

Dependent clause and subordinate clause mean the same thing, yes.

A clause can refer to a sentence, a part of a sentence, or a word.

I'd've have thought (and I am by no means an expert!!!) that it was more of an idiom than a collocation.

But what I mean is that in this case it's not dependent on anything. A subordinate clause needs a main clause in order to make sense (as inthe example I gave, where the conditional clause makes no sense without a main clause), whereas here you can use the expression on its own, for example as an expression of frustration 'Oh for Pete's sake!'.

Or am I wrong?