From the same as 'agam; a marshy pool (others from a different root, a kettle); by implication a rush (as growing there); collectively a rope of rushes -- bulrush, caldron, hook, rush.
see HEBREW 'agam
H100. agmon
אַגְמוֺן אַגְמֹן, noun [masculine] rush, bulrush.
1 used as cord or line Job 40:26 (of twisted rushes, or spun of rush-fibre, compare Di on the passage); as fuel Job 41:12; simile of bending head Isaiah 58:5.
2 metaphor of the lowly, insignif. ("" כִּמָּה) Isaiah 9:13; 19:15.
אגן (probably circular, round, compare Arabic ball of cheek & see Talmud אוֺגֶן curved rim of a vessel).