How to classify the non-standard reading of "お土産{みやげ}"?

Question

Is お土産{みやげ} an 当{あ}て字{じ}、 熟字訓{じゅくじくん}、 or something else?

For 「お土産」 to be 当て字, the「み」reading must be part of the 音{おん}、訓{くん} readings or a 名乗り{なのり} reading for the「土」kanji. This is not the case.

For 「お土産」 to be 「熟字訓」, the meaning of the characters 「土」and「産」when placed side-by-side must approximate the meaning of "souvenir". And this is not the case.

So, is the reading of 「お土産」 classified as "non-standard", but not in the sense of 「当て字」 or「熟字訓」? Maybe there is a 3rd classification for words with non-standard readings? Is this 3rd classification maybe "難読{なんよ}み" (I've found very little info about 難読み so far).

Answer 1

I think you might be getting deceived by the English word "souvenir" in thinking 土 + 産 has no meaning connection to みやげ. The English word tends to mean something you buy for yourself to remember your travel. The Japanese word is for things you buy to give to others that reflect the cuisine of where you travelled.

産 means either to birth a child or to produce goods or the goods necessary for life.

And 土 means earth, dirt, and some other things but particularly relevant is that it means 地方 ("geographic area" but much more colloquially used than the heady-sounding English equvalent). [Thanks snailboat for the improvement!]

Seems like a 熟字訓 to me. Moreover, the Japanese Wikipedia specifically lists it as one stating:

その土地の特産品、旅先で仕入れた品物、記念品。土産物（みやげもの/どさんぶつ）。

Answer 2

Shogakukan's Kokugo Dai Jiten Dictionary has this to say about the etymology of みやげ (my additions in [square brackets]):

「みあげ」の変化で、「みあげ」は「見上げ」、すなわち、よく見て、人に差し上げる品の意という。あるいは「御（み）上げ」か。「どさん（土産）2」と意味が近似するところから「土産」の字を当てる
A shift from miage, where miage means 見{み}上{あ}げ, in other words, to look something over and then give it to someone. Alternately, may be from 御{み}上{あ}げ [where the mi is an honorific]. The spelling 土産 is used given the similarity of meaning with sense 2 of 土産{どさん}.

That sense 2, a gift [for others] from an area where one has visited, arose as an extension of the kanji-based meaning of product of a specific area.