While vs Whilst

Yes.

Do you want to know under what circumstances?

I always thought it was a British thing.

You're mostly right, pedant. However, as the immigrant population in the USchanges, there are more and more people here who were educated to use British english and one sees it occasionally.

Now that SOMEONE

that should be 'I saw him whilst waiting for a train', you don't need the 'I was'

Sounds to me like the 'st' in whilst represents the tail-end of a substantive verb, hence the absence of 'I was' in the example. Can anybody confirm or correct this?

As a rule of thumb, whilst is used when the verb the follows is a form of 'to be', as in "whilst I'm ... ", "whilst he was".

I personally think it sounds best when you drop the "I was" or "they were" etc. off, but I don't think that's got anything to do with the -st.

I've always thought that "whilst" (instead of "while") and "amongst" (instead of "among") were exclusively British.

Same here, but I have always thought that "whilst" was on the slow road out of common English usage.

"Amongst" and "among" both seem to occur in American English however. Whilst "whilst" seems very King James.

Is there anything like whilst should be used in between the sentence and while should always be at the beginning?or vice versa? like for example: While i was planning to go... or I saw hime whilst waiting in the bus stand.

No there is no rule.The two words have the same meaning, 'whilst' is the older version (some dictionaries list it as obsolete) and it usually appears only in formal or poetic writing.

If you stick to 'while' you won't ever be wrong, whereas 'whilst' can easily look out of place.