Seichel means wit or intelligence. In the expressions, use a bit of seichel, or pity they dont teach you seichel at that university of yours, its roughly synonymous with nous, noddle or common sense. Modern Hebrew uses the expression sechel hayashar for common sense.
Seichel is derived from the word meaning to be bright or see clearly. In the Bible the wise or enlightened are known as maskilim, from the same root. The maskilim are said to shine like the sky (Daniel 12:3), and King David was described as maskil in all his ways.
In the late 18th century the Jewish strain of the European Enlightenment called themselves maskilim, and their movement the haskalah.
The early maskilim in Eastern Europe were religious Jews whose innovativeness consisted of reading secular literature and trying to revive Hebrew as a spoken and written language.
As the haskalah moved westwards, it became especially associated with Moses Mendelsohn and his circle.
Mendelsohns contemporaries wrote in Hebrew, but the next generation of maskilim became cut off from Jewish sources and wrote in German.
Many of them assimilated or converted to Christianity. Haskalah became irrelevant to the Jewish masses and disappointed the hopes vested in it for a renewal of Jewish life.