Boyd’s Bible Dictionary:

(his excellence). Honorary title (Ex. 3:1), of Reuel (Ex. 2:18), or Raguel (Num. 10:29), the father-in-law of Moses (Ex. 18).

Concise Bible Dictionary:

Father-in-law of Moses, and a priest of Midian, with whom Moses spent forty years of his life. He brought to Moses his wife and their two sons soon after Israel had left Egypt. He advised Moses to appoint judges for minor cases. He rejoiced and blessed God for the deliverance He had given to His people, and said, “Now I know that Jehovah is greater than all gods: for in the thing wherein they dealt proudly he was above them.” He also took a burnt offering and sacrifices for God: and Aaron and all the elders of Israel came to eat bread with him before God. He thus prefigures the joy of the Gentiles in the Lord’s salvation and deliverance witnessed to them in His dealings with Israel (Deut. 32:43; Psa. 67; Psa. 117). He departed again to his own land (Ex. 3:1; Ex. 4:18; Ex. 18:1-12).
He is apparently called REUEL in Exodus 2:18; and HOBAB in Numbers 10:29, where RAGUEL is REUEL in the Hebrew. This passage says that Raguel, the Midianite, was the father of HOBAB, the father-in-law of Moses (see also Judg. 4:11), so that in Exodus 2:18 “father” may signify “grandfather.” Hobab may have been the personal name, and Jethro an official name. In Judges 1:16 Moses’ father-in-law is called a Kenite, but the exact signification of this term is not known.

Strong’s Dictionary of Hebrew Words:

from 3499 with pron. suffix; his excellence; Jethro, Moses' father-in-law
KJV Usage:
Jethro. Compare 3500

Jackson’s Dictionary of Scripture Proper Names:

: his remnant: his excellence

Potts’ Bible Proper Names:

Very excellent; his excellence:―father-in-law of Moses [JETHER], Exod. 3:1. {Valde excellens}