The Origin Of The Word "MANDARIN"

"Mandarin" is not strictly the name of a language, although it refers to one.
"Mandarin" is a Portuguese word borrowed from Malaysian which is influenced by Sanskrit
“Mantrin”, which means "court official, counselor",
So Portuguese colony call this language as Mantrin Language.

the interpreter use the translation "mantrin" [using malay language: manteri, which means Minister or Counselor] when translate the language that used in that era to Portuguese Colony, it was 官話【官话 guān huà】 which mean "the language of court officials"

this 官話 would be equivalent to calling a Western language "standard", where "standard" could refer to whatever language happens to be the standard at the time, as the translation from the original language官話【官话 guān huà】

There’s source said that Mandarin is originated from the Chinese characters
滿大人【满大人 mǎn dà rén】 but it's better we consider for these reasons:

1. 滿族【满族 mǎn zú – Manchurian】 The language of Manchu ethnic group which originated from Liaoning province is not refer to which nowadays so called Mandarin as their native language, but Manchurian speaks Tungusic languages, even their writing is not using Chinese characters, for example: ᡶᡠᠯᡤᡳᠶᠠᠨ; and they are minority ethnic group.

Note:
Tungusic language has many branches of language,
they are mixing between Jurchen, Hezhen / Goldi language and Russian language that use in Siberia and also any other native Russian language such Udihe, etc.

And this language [Tungusic] is used in ancient China by 靺鞨【Mogher】people, 靺 is an adjective, which mean Barbarian【匈奴 xiōng nù】which in Southern Fujianese / Southern Min language 【闽南语】is called 番仔【fān zǎi; in Southern Min dialect is pronounced as “Huan A”】because 靺 、匈奴、番仔 means Persians or Barbarian, meanwhile 鞨 in ancient Chinese language used to refer a stone.

Before the period of 秦漢【秦汉qín hàn】- 221 SM【around 3th century BC】, 中原人 consider people who make a living by Husbandry [animal husbandry], included the poeple in western regions of “City State” all of those person are to be known as “胡” hú.

Note:
【中原人 is the people of areas in the Yellow River, including most parts of Henan, Shandong, western and southern Hebei and hanxi.】
[City State is a city in ancient China, silk road are also inside this place]
胡 [hú] in ancient Chinese language refer to the meaning of
蠻夷【蠻夷mán yí - Barbarian】and also called as
番仔【番仔fān zǎi – aborigine】，or
番邦【番邦fān bāng – non Han】.

2. Mandarin at the beginning was originated from Nan Cing 南京 and Pei Cing北京 dialect [much of Pei Cing 【pīn yīn: běi jīng, now become the capital of China】 dialect still being used until now in Taiwan 台灣]. This Nan Cing and Pei Cing language first used as "the language of court officials" since Ming Dynasty [By Mongol, not Manchu].

3. The most important thing we should consider is since Ming Dynasty, no one ever called this language as Mandarin. It is FOREIGN TERM. Not Chinese term.

4. This so called MANTRIN Language by Portuguese Colony was spread out to out of China [to Europe], so SINCE THEN, international people have known this language as Mandarin that was brought by Portuguese, and this MANTRIN form was later on changed become Mandarin.

you can also visit this page as additional
http://tieba.baidu.com/f?kz=122245966

There have been several history of ”guān huà”, the present one that Westerners call Mandarin has been in use since as early as the Southern Song dynasty, (1127-1279) but Westerners only encountered it during the Ming and Qing dynasties.

Nowadays of Mandarin,
“普通话 pǔ tōng huà”，“国语”，or “中文 zhōng wén” as it is called locally,
is a *composite* of other languages, mainly the Han language,
which has been around as long as the Han people 【漢族、汉族、hàn zú】themselves,
since antiquity. It also incorporates other northern dialects.

Strangely enough, you won't hear the word "Mandarin" used in PRC 【中国】
Because it is foreign term to call this Chinese Official language. even Chinese people Won’t acknowledge it as 满大人[Noble or Master Manchurian] language.

The term for the language *in* Mandarin, as mentioned above is
“普通话 pǔ tōng huà” ； “汉语hàn yǔ”；“中文 zhōng wén”
or in formal contexts “国语 guó yǔ” (the national language).