For examples;
Q1)
Why the O-Bon festival and O-Bon tray are described
with the same Kanji 
or Bon?"
A1)
"Bon " of Bon tray is originally a
Japanese word corresponding to "tray"
in English. But "Bon "
of Bon festival was born as follows:
1) A
Buddhist event "ullambana (Sanskrit)"
had originally existed in India.
2) Chinese people transcribed the
"ullambana" to three or four Kanjis 
.
3) Japnese people used the same Kanjis
and pronounced them Urabon or Urabon-e and
abbreviated it to or Bon.
Q2)
Why do Japanese people eat the eel on Doyo-no-Ushi 
day?
Why not beaf?
A2)
There are two traditions: 1) Hiraga Gennai (an
old Japanese scientist) said, "The eel is a
medicine for sunstroke." 2) Someone said,
"To eat foods, which the names start from U,
on the Ushi-day is good for our health."
Such foods were Unagi(eel), Uri(melon),
Udon(wheat noodle), Ushi(beef), and etc. Most of
us chose the eel because it was good taste and we
were banned to eat four-leg animals like canttle
before Meiji.
Doyo
is the last 18 days
of each season (in this case, the season is
summer.) It is, in other words, 18 days just
before the first day of fall. (My dictionary
states that the period of Doyo is 18 days but the
period fluctuates between 17 and 19 days every
year on the calendar. I do not know why the
descriptions on the dictionary and the calendar
are different. My knowledge about the lunar
calendar is not enough.) The fall of this year
begins on August 7. So the period of Doyo is from
July 19 to August 6 (cf. the calendar on the next
page. The Doyo of this year is 19 days.)
Ushi
is the second member of 12 Kanji
characters, which are called Junishi. The 12
Kanji characters are used to describe directions
and hours. Ushi meant the direction,
north-northeast, and the time, between 1:00 and
2:00 a.m. As same as usual Kanji, Ushihas
two (or more) pronunciations, "Chuu"
and "Ushi." Originally it did not mean
the cattle. When we began to count years and
dates with Junishi, we corresponded Ushi to
homonym 
Ushi, or the cattle, so that we could
easily memorize it. The other 11 Kanji characters
were also corresponded to 11 animals' names.
According to the calendar used Junishi
,
July 28, 2005 is the Ushi-day to eat the eel.
(cf. the
following calendar)