Ibn Ezra

They take their stand (יִ֥תְיַצְּב֨וּ - yityatzvu): The kings and the regents (roznim - also nobles/rulers) [act] together with the nations [mentioned in v. 1]. And nosdu-yachad (נוֹסְדוּ־יָ֑חַד - they intrigue/conspire together): [Nosdu] is from the root sod (סוֹד - secret, council, conspiracy). Behold, this follows the pattern of (Psalm 35:1) "Contend (Rivah), O LORD, with those who contend with me (yerivai)," where [yerivai] is from the root rav (רב - contend, strive), which is a hollow root (me-'alumei ha-ayin - i.e., middle root letter is Vav or Yod) related to the noun riv (רִיב - strife). [Ibn Ezra implies a similar relationship between the verb nosdu and the noun sod]. The yod in yerivai is transformed and it represents a defective adjectival form. Alternatively, [nosdu] is from the root yesod (יְסוֹד - foundation), [implying they establish a common foundation or plan together]. According to the opinion that this psalm, which the poet composed, was said about David (or that he [David] prophesied about himself)—behold, we find that many nations were under David's control [making such a rebellion historically plausible]. And if [the psalm is] about the Messiah, the matter [of widespread opposition] is even clearer. And the meaning of "against the LORD" ('עַל־ה - al Ad-nai): Is that they have departed from the control of the sound judgment (sikul ha-da'at) which God implanted in the heart of every person. And [the meaning of] "and against His anointed" (וְעַל־מְשִׁיחֽוֹ - ve-al meshicho): Is that they should not deny him [or 'deal falsely with him'], but rather submit (yasuru el) to his authority/obedience (mishma'ato) to pay him tribute (mas).