Yes, that is the correct possessive form of the singular noun toothbrush. example: Don't buy that one, the toothbrush's cover is cracked.
The noun form for the adjective horrible is horribleness.
The noun form of the adjective obedient is obedience.
The noun form of the adjective 'prosperous' is prosperousness.A related noun form is prosperity.
The noun form of "punish" is "punishment."
The noun form of "religious" is "religion."
The noun form is the act of demanding, or something that is demanded, the word you need in 'demander
The noun form of "acrimonious" is "acrimoniousness."
The noun form for the adjective glaring is glaringness. Another noun form is glare.
The noun form for the adjective austere is austereness. Another noun form is austerity.
Implication is the noun form of "imply."
ability is the noun form of the adjective able;conversation is the noun form of the verb to converse;dependence is the noun form of the verb to depend;departure is the noun form of the verb to depart;dwelling is the noun form of the verb to dwell;favorite is the noun form of the verb to favor;happiness is the noun form of the adjective happy;information is the noun form of the verb to inform;rarity is the noun form of the adjective rare;weakness is the noun form of the adjective weak;writer is the noun form of the verb to write;writing is also a noun form of the verb to write.