Bonsai or Bonsai tree.
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I believe Bonsai could be characterized by "Solid, misshapen, sad" (that was my first read of the phrase)
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The qualities a bonsai tree and a linguistic object have in common are: object acted upon by subject (linguistic object: that acted upon by subject (wiki: Traditional grammar defines the object in a sentence as the entity that is acted upon by the subject.There is thus a primary distinction between subjects and objects that is understood in terms of the action expressed by the verb, e.g. Tom studies grammar...)
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The qualities a bonsai tree and a linguistic object of rare beauty have in common are
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1) object acted upon by subject
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2) individuality and beauty.
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I believe the bonsai tree has individuality and possesses a rare beauty. A tie between bonsai tree and a linguistic object is rare beauty if the linguistic object is unique to an individual speaker - in other words, idiolect.
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In linguistics, an idiolect is an individual's distinctive and unique use of language, including speech. This unique usage encompasses vocabulary, grammar, and pronunciation. Idiolect is the variety of language unique to an individual. (wiki: hxxp://en Wikipedia org wiki Idiolect).
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A linguistic object of rare beauty is in fact an idiolect I would argue that language unique to an individual possesses a rare beauty.
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In fact, at another level, consider: "Bonsai" is a unique linguistic construction itself (plantings in tray, from bon, a tray or low-sided pot and sai, a planting or plantings) that I would consider rare and beautiful: "...a Japanese pronunciation of the earlier Chinese term penzai. A "bon" is a tray-like pot typically used in bonsai culture. The word bonsai is often used in English as an umbrella term for all miniature trees in containers or pots..." (wiki)
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This connection, analogy or commonality is reflected in at least one instance of its usage: "I say language but Gaelic isn’t one, not really. Its vocabulary is tiny, with no form of saying yes or no and attuned to a distant, pre-technological world. It’s essentially a kind of rural patois, a bonsai idiolect; a way of specifying concepts central to a particular, highly codified way of life..." (google for "bonsai idiolect"; there are many hits).
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thus, the answer is the word itself bonsai and what it actually represents - physically and culturally.
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finally (ahem) barking up the wrong tree...
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very nice!