When I look up some kanji without ON reading like 皿, my dictionary properly states just its KUN reading (sara) and examples that use it. But WWWjdic and other online sites say it has an ON reading (bei in this case).
Where did this come from?
I don't see it used at all in examples like on: http://www.mahou.org/Kanji/3B2E/?example#example
Then I look it up on wiktionary,
http://en.wiktionary.org/wiki/%E7%9A%BF
and it gives yet another ON reading (myou). Which makes me even more confused.
I am Japanese but I don't know ON reading of 皿.
So I feld for it.But I found only example 器皿.
I think You seem to know about 器.
器 means container,redeptacle or vessel.(ONreading:KI KUNreading:UTUWA)
器皿 means dish.(Reading:KIBEI noun phrase)
Type of same meaning KANJI combination.
I think KIBUTU don't used common in japanese.
If you look and read this kanji in japan.
Maybe you will see using examples 磁器皿(china),陶器皿（pottery）,和食器皿（dishes for Japanese food）etc.
Then you should read JIKIZARA,TOUKIZARA,WASHOKKIZARA.
(Note that the explanations below are scholastically inaccurate.)
To be exact, there are a few variations in the system of ON reading: Go-on(呉音), Kan-on(漢音), To-on(唐音) and kanoyo-on(慣用音).
http://en.wikipedia.org/wiki/Go-on
http://en.wikipedia.org/wiki/T%C5%8D-on
In simple terms, Go-on is old ON which was imported from China or other contries in 5th century. Kan-on is of 7th century and To-on is of 12th century. 慣用音(idiomatic ON) is "Japanized" ON, or arranged ON to fit for modern Japanese in around 19-20th century.
In 皿's case,
Kun-yomi: sara
Go-on: myou, myau
Kan-on: mei
Kanyo-on: bei
Not all kanji has all of kun, Go, Kan, To and kanyo since some of those ON don't exist, or vanished and are not used today. The judgement of vanished or not vanished depends on editors of each dictionary. Japanese wiktionary listed Kun, Go, Kan and Kanyo for 皿. English wiktinary listed only Kun, Go and Kanyo. Maybe your ditionary considers all of them except Kun were vanished.
Below My idea about ON reading "BEI".
Plate forms circle and flat at a guess.And it's colored white.
I think resemble sound of "BEI" and "HEI".
KANJI is satisfied above of terms is "幣"and"餅".
幣 is used about 神道（Shinto）originally.
"circle"+"flat"=coin.幣 was meaned money after. ex:紙幣（papermoney)貨幣（coin money)
餅 means rice cake.Do you know it?
餅（KUNreading:MOTI ONreading:HEI)is white,flat and circle.
In this connection,MOTI made from rice.rice is 米（ONreading:BEI KUNreading:KOME)
Icome to think of it,rice also white and flat and circle.
This is my arbitrary idea.
Maybe,sound of HEI or BEI meaned "white""circle""flat"things at early Japanese.
Lastly,I apologize to you for my poor English.
>>2
Thanks, those are nice examples.
It took me a while to find 器皿 in an online dictionary. It's not in a lot even though it produces a lot of hits on google. I found it on yahoo's dictionary though.
>>3
Thanks for clearing it up. It seems that my dictionary is very liberal about this and doesn't give, what seem to be, vanished/archaic readings for a lot of things. I think this is because it's specifically for learning as opposed to a reference so they don't want to bother you with it.
>>4
This falls under etymology right? I think etymology is really interesting.