Korah's rebellion = Despising the Word of the Lord

The Complete Word Study Dictionary: Old Testament 5006. נָאַץ nāʾaṣ

5006. נָאַץ nāʾaṣ: A verb meaning to revile, to scorn, to reject. It is related to nāṣaṣ (5340), meaning to scorn or to blaspheme. This word often refers to rejecting the counsel of a wise person. This scornful attitude results in an unhappy life: people live in affliction because they reject God’s counsel (Ps. 107:11). Another example of a passage that uses this word is Proverbs 1:30, where wisdom laments that people scorn her reproof. In another instance of this word, the Israelites were chastised because they had rejected God’s Law (Isa. 5:24).

Numbers 16:30 ASV

But if Jehovah make a new thing, and the ground open its mouth, and swallow them up, with all that appertain unto them, and they go down alive into Sheol; then ye shall understand that these men have despised Jehovah.

5 .  נָאַץ   nāʾaṣ :  A verb meaning to revile, to scorn, to reject. It is related to  nāṣaṣ  ( 5340 ), meaning to scorn or to blaspheme. This word often refers to rejecting the counsel of a wise person. This scornful attitude results in an unhappy life: people live  in affliction because they reject God’s counsel ( Ps. 107:11 ). Another example of a passage that uses this word is  Proverbs 1:30 , where wisdom laments that people scorn her reproof. In another instance of this word, the Israelites were chastised because they had rejected God’s Law ( Isa. 5:24 ).

God says that Korah despised the Word of the Lord especially from the mouth of another man!

It was rebellion:

(qûm). vb. to rise. The core meaning of this verb is “to stand up” or “to rise” in a physical sense; related to the concept of rebelliousness, it can also mean “to rise up” (against someone).

The verb qûm appears frequently in the OT, though it does not often appear with the sense of rebellion or confrontation. Examples of this use of the verb include the rebellion against Moses and Aaron by the Israelite chieftains and by Dathan and Abiram (Num 16:1–35) as well as Jeroboam’s rebellion against Solomon (2 Chr 13:6).

New Testament

ἐπανίσταμαι (epanistamai). vb. to rise up, to rebel. This verb literally means “to rise”; figuratively, it can describe the acts of revolting or rebelling.

Bianchi, F. (2014) “Rebelliousness,” Lexham Theological Wordbook. Edited by D. Mangum et al. Bellingham, WA: Lexham Press (Lexham Bible Reference Series).