Is there any difference between the two words ? Which one is more formal than the other one and which one do English natives use most?Why?
I admit [ but I can`t explain why] that "till" sounds to me as an unfinished word.Can I use them as follows?
a] I`ll be there till Friday .
b] I`ll be there until Friday.
c] I`ll be there by Friday.
Are these sentences correct?
What is the difference [if any] among [a] , [b] and [c] ?
"Until" is an interesting word, as it consists of the Old Norse "und" plus the Old English "til", both of which meant "till". So the meaning is duplicated.
However, there is a general notion that "till" is a shortened form of "until" so you often see it written 'til.
There are some set phrases in which only one can appear (e.g. "till death do us part", "unless and until"); but on the whole, they are interchangeable. However, if the "until/till" clause begins the sentence, it's much more usual to use "until", e.g.
1. Until today, I had never met a Russian tightrope-walker.
2. Until you learn to behave yourself, I'm confiscating your remote control.
"Until" is now more likely to be found in a formal context; though "till" is very common in poetry, for metrical reasons.