Albert Barnes Commentary Proverbs 30:31

"The greyhound; the he-goat also; And the king against whom there is no rising up." — Proverbs 30:31 (ASV)

A greyhound - The Hebrew word occurs nowhere else in the Old Testament. The literal meaning is: “one with loins girded;” and some have referred this to the stripes of the zebra, others to the “war-horse” (compare Job 39:19, Job 39:25), as he is represented in the sculptures of Persepolis, with rich and stately trappings.

A king, against whom there is no rising up - i.e., a king irresistible. Others prefer, “a king in the midst of his people,” and the sense, as giving a more vivid picture, is certainly more satisfactory.