From an unused root meaning to tie up; a stall (for cattle) -- X fat(-ted), stall.
H4770. marbeq
מַרְבֵק noun [masculine] stall (literally tying-place); — מ מִתּוֺךְ ׳עֲגָלִים Amos 6:4 calves out of the stall (where they were fattened); ׳עֵגֶלמֿ 1 Samuel 28:24 i.e. a stall-fed, fatted, calf; so מ ׳כְּעֶנְלֵי Malachi 3:20 (simile of prosperity), Jeremiah 46:21 (simile of well-fed and arrogant mercenaries).