ارك
Attested forms : ٱلْأَرَآئِكِ 5
Core meaning
The adorned couch: the seat of honoured rest, where one reclines in the Garden and from where one looks on.
Uses
عَلَى ٱلْأَرَآئِكِ with مُتَّكِـِٔين → "reclining on adorned couches" : the rest of those who have received the Garden.
عَلَى ٱلْأَرَآئِكِ with a gaze → "on adorned couches", "upon adorned couches" : the place from which the virtuous observe, and from which they laugh at those who laughed at them.
Evidence from the text
The five uses describe the Garden, and the word is never alone there: it carries a posture, that of peaceful reclining (18:31, 36:56, 76:13), or a gaze (83:23, 83:35). The adorned couch is not a piece of furniture described: it is the place of one who has nothing more to fear.
Sura 83 makes it the place of a reversal. In this world, those who cut themselves off "used to laugh at those who believed" (83:29) and winked at one another as they passed; on the appointed day, "those who believed are laughing at the disowners, upon adorned couches" (83:34-35), and they look whether these have received the return of what they used to do (83:36). The laughter changes sides, and the adorned couch is the seat from which one witnesses it.
See also
وكء (to recline) · ضحك (laughter)