English expressions (idioms) about days don't map directly to French expressions. Whereas English says "on Thursday", French would simply say "le jeudi". E.g., Quel jour est la fête ? La fête / Elle est samedi. = What day is the party? It is on Saturday. http://french.about.com/od/grammar/a/dates_2.htm So the idea to take away from this is that just because English says "on" does not mean there must be a corresponding word in French.
Where are come from the days of the week in the French language ?
LUNDI it's LUNAES DIES, day of the LUNE
MARDI it's MARTIS DIES, day of MARS
MERCREDI it's MERCURII DIES, day of MERCURE
JEUDI it's JOVIS DIES, day of JUPITER
VENDREDI it's VENERIS DIES, day of VENUS
SAMEDI it's SABBATI DIES, day of SABBAT. That we indicate to ourselves directly the week has a Hebraic origin. In English, Samedi is SATURDAY, the day of SATURNE. Indeed, in French, is easier to say SAMEDI than SATURDI. But, that would have be only an usual question.
DIMANCHE it's DIES DOMINICA, the day of Lord. The first christians substituted this denomination day of SUN's. Religion oblige ! In spanish, it's DOMINGO. In English or in German, we still find SUNDAY and SONNTAG : day of SUN.
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According to my brief research on the internet, the word til or till is older than the word until. It is not a contraction of until, though many people think it is. The oldest spelling is til, the modern spelling is till. (For most one-syllable words ending in s, f, or l the s, f, or l is doubled.) People who think it is a contraction sometimes spell it 'til. Many dictionaries and spell checks will only accept the standard modern spelling till, although all spellings are in common use. Whichever spelling you use, there will be some people who are absolutely sure you are wrong, so if you are writing something important it's safest to just use until.
'Til, till, until are all accepted variations and you may be surprised to learn that, in fact, "till" is quite correct as a short version of "until". http://dictionary.cambridge.org/us/dictionary/english/till Even so, it's better to simply say, "See you Thursday!"