وَجَعَلُوا۟ لِلَّهِ أَندَادًا لِّيُضِلُّوا۟ عَن سَبِيلِهِۦ ۗ قُلْ تَمَتَّعُوا۟ فَإِنَّ مَصِيرَكُمْ إِلَى ٱلنَّارِ
"They set up equals to God — in order to lead astray from His path. Say: 'Enjoy yourselves, then; your journey's end is to the Fire.'"
The plural of nidd. The root ن-د-د: to be a thing's equal, its like, its counterpart; and from there the sense of "to flee, to take fright and scatter."
The lexicographers record a distinction between nidd and mithl: mithl is likeness in general, while nidd is an equal set opposite, counted as a rival. That is, the word conveys not a resemblance but a setting over against.
The word had occurred at al-Baqara 2/22 (fa-lā tajʿalū li'llāhi andādan wa antum taʿlamūn) and was treated there. I rely on that treatment.
The imperative here does not convey a command. In Arabic this is called tahdīd (a threat in the form of a command) and it has been treated in several places in the series (iʿmalū mā shiʾtum at Fuṣṣilat 41/40, kulū wa tamattaʿū qalīlā at al-Mursalāt 77/46). I rely on those treatments.
What must be recorded is the second half of the sentence: fa-inna maṣīrakum ila'n-nār. The command is given together with its ground — and the ground annuls the command from within. I record this as an observation about the word order: when "enjoy yourselves" and "your journey's end is to the Fire" stand in the same sentence, the first half becomes not a permission but a statement of measure.
م-ص-ر / ص-ي-ر — maṣīr: the place one arrives at, the place of return. The root ص-ي-ر: to turn from one state into another.