Thaddeus has a genuinely debated root, with proposals linking it to a word for "heart" or "courage" on one side and to "praise" on the other, with no consensus among scholars. Both readings converge on something admired -- either bravery itself or the recognition that tends to follow it.
If in any nativity Mercury shall be in the ascendant, oriental, and swift; the native will be eloquent, and learned in the liberal sciences: the same happeneth, if he shall be in Sagittarius in his proper terms. - William Lilly (1602.-1681.)