A and B are standing in the living room, A behind a couch and B in front of it. B’s shoes are on the floor behind the couch where A can see them but B cannot. B says to A, “Where are my shoes?” A replies, “They’re subind the couch.”
α is subind β means that α is concealed by β for the listener but not the speaker. It is pronounced /sʌbaɪnd/ and functions syntactically as a preposition. Like other prepositions its meaning is relative to the immediate physical context of the utterance. Unlike on, above, in etc., the point of reference is not the internal argument β but two lines of sight. If A and B switched places, A could no longer say that the shoes were subind the couch, though he could say they were behind it from anywhere in the room.
Subind’s semantics is similar to proximal/distal relationships in that it is a function of the interlocutors’ positions. English’s here/there and Spanish’s aqui/allí/allá are examples. Korean has a three-way distinction 이/그/저 based on the relative locations of the object, speaker, and listener. Unlike these, however, subind’s deixis involves the interlocutors’ ability to see the subject α of the preposition. This relative capacity vis-a-vis β is all that matters, not the locations of A and B or the structure of β itself. (So the fact that a couch has a front and a back side is irrelevant.) Irrealis intrudes in the form of ways the relative visibility of β is likely to change in the near future. If neither A nor B can see the shoes and A says “Maybe they’re subind the couch” this implies that he intends to go check behind the couch soon. (Much like “Let me check behind the couch”, which, note, is a statement of intent, not a request for permission.) Whether “Maybe they’re subind the couch” is permissible when A is heading behind the couch for the express purpose of finding the shoes or only in a scenario where A was already planning to go there for some other reason is a point of contention even among native speakers.
The literal meaning of subind has to do just with obstructed sight lines and not with any sense of intentional concealment, but those shades of meaning are all accessible via metaphor. If I recently moved the scissors from their customary location to the top drawer, I might answer your inquiry about their location with “They’re subind the top drawer” as a way of jokingly acknowledging the fact that I just made it difficult for you to find them. (The same as if I had said “I hid them from you in the top drawer”.) Metaphor also gives access to more abstract notions of concealment. I say “John’s vindictive nature is subind an air of superficial friendliness” when you think John is a good guy but I can see right through the S.O.B. By itself subind has no connotations of deception. If “Susan’s self-interest is subind a smile” Susan may be merely oblivious, but if I throw a little agency into the mix and say “Susan is putting her self-interest subind a smile” I am calling her a liar in no uncertain terms.
Does the meaning of this preposition strike you as unusually complicated? This is an illusion. Subind’s perfectly ordinary semantics is subind your familiarity with the equally-nuanced meanings of prepositions you use every day.