Read the passages. 16 is referring to his loins, 17 is referring to his loins. The meaning of ‘tail’ is obvious.
15 “Look at the behemoth, [a]
which I made along with you
and which feeds on grass like an ox.
16 What strength he has in his loins,
what power in the muscles of his belly!
17 His tail [b] sways like a cedar;
the sinews of his thighs are close-knit.
But the LORD said to Moses, "Stretch out your hand and grasp it by its tail"--so he stretched out his hand and caught it, and it became a staff in his hand-- - Exodus 4:4The meaning of the word is obvious. It means "tail".
The LORD will make you the head and not the tail, and you only will be above, and you will not be underneath, if you listen to the commandments of the LORD your God, which I charge you today, to observe them carefully, - Deuteronomy 28:13
He shall lend to you, but you will not lend to him; he shall be the head, and you will be the tail. - Deuteronomy 28:44
Samson went and caught three hundred foxes, and took torches, and turned the foxes tail to tail and put one torch in the middle between two tails. - Judges 15:4
"He bends his tail like a cedar; The sinews of his thighs are knit together. - Job 40:17
and say to him, 'Take care and be calm, have no fear and do not be fainthearted because of these two stubs of smoldering firebrands, on account of the fierce anger of Rezin and Aram and the son of Remaliah. - Isaiah 7:4
So the LORD cuts off head and tail from Israel, Both palm branch and bulrush in a single day. - Isaiah 9:14
The head is the elder and honorable man, And the prophet who teaches falsehood is the tail. - Isaiah 9:15
There will be no work for Egypt Which its head or tail, its palm branch or bulrush, may do. - Isaiah 19:15