This is the 879th most frequent Polish word.
nikt
"Nobody" or "no one."
Here, 'nikt' is used to reference an absence of someone (anyone) taking the action of helping the speaker.
Nic nie rozumiałem, dlatego nikt mi nie pomógł.
I didn't understand anything, which is why no one helped me.
In this instance, 'nikim' is an inflected form of 'nikt', used in the instrumental case to indicate action involving no specific individual.
Zapytaj o to, ale z nikim o tym nie rozmawiaj.
Ask about it, but don't talk to anyone about it.
In this sentence, 'nikt' acts as the subject of the sentence and means 'no one', as it refers to an undefined person who did not appear.