The Hebrew word ṣə·ḏā·q actually occurs in three forms in Jer 33:15, 16 as follows:
- v15a - "righteous branch", צְדָקָ֑ה (ṣə·ḏā·qāh) is Noun feminine singular, which acts as an adjective for "branch" and is obviously a Messianic prophecy.
- v15b - "execute justice and righteousness on the earth", וּצְדָקָ֖ה (ū·ṣə·ḏā·qāh) is Conjunctive waw + Noun, feminine singular, describes the type of government of Messiah. Apart from the conjunction "and" it is the same part of speech but now the noun is a stand-alone noun (not used as an adjective).
- v16 - "The LORD is our righteousness", צִדְקֵֽנוּ׃ (ṣiḏ·qê·nū) is Noun, masculine singular construct, first person common plural, is used as the title of Jerusalem when it is administered by Messiah.
The flow of thought is interesting here. Beginning with the prophesied new King, Messiah, He is given the title, "Righteous Branch"; His administration is known for its justice and righteousness; so much so that the city (Jerusalem) becomes known by the title, "The LORD is our righteousness".
It will be noticed that, while this reproduces the language of
Jeremiah 23:6, it does so with a remarkable difference. There the
title, "The Lord our Righteousness," is given to the future King, and
the passage has accordingly been used as a proof of the full divinity
of the Christ, who is that King. Here it is given to the city, and, so
given, can only mean that that name will be, as it were, the motto and
watchword of her being. She will be a city marked by a righteousness
which will be the gift of Jehovah; He will inscribe that name on her
banners, and. grave it on her portals. It is obvious that this throws
light on the meaning of the title as applied to the King.