(Aramaic) from an unused root corresponding to rakab (in the sense of bending the knee); the knee -- knee.
see HEBREW rakab
H755. arkubah
[אַרְכֻבָּה] noun feminine id. (by transposition; compare ᵑ7 רְכוּבָא, ᵑ7J אַרְכּוּבְתָּא; Christian-Palestinian Aramaic SchwIdioticon 89 (who > explained from √ רכב, compare SchulthLex.194); Arabic id.); — plural suffix אַרְכֻבָּתֵהּ Daniel 5:6 his knees.