The noun rub is a singular, common noun; an abstract noun for something that gets in the way, a difficult situation; a concrete noun for the act of rubbing (massaging or polishing).
rub is not a verb that is a noun
Kill them.
Noun. It is a person. Remember the definition of a noun.
Definition is a noun.
The noun forms of the verb to define are definition and the gerund, defining.
nuzzel means to push against or rub with your nose
A sudden disabling attack, or to rub something very gently.
Definition
Yes, the word 'definition' is a singular, common, abstract noun; a word for statement of the meaning of a word, phrase, or term.
The corresponding noun to the verb define is definition
A noun is a word for a person, place, or thing.
The noun stifle is the rear 'knee joint' of a horse.