To clarify a sadly nonsensical
Webster 1913 definition, a precept is a rule of personal
conduct, like a
principle, or a religious rule of behavior, like a
doctrine or perhaps a
commandment. Essentially, a precept dictates appropriate behavior in a situation. The word derives from the
Latin praecipere, to advise or teach.
Unfortunately, according to dictionary.com, Webster's Revised Unabridged Dictionary of 1996 still has this same entry!
Source: http://www.dictionary.com/cgi-bin/dict.pl?term=precept