Sell is not an adjective, it is a verb to 'sell'.
The adjective form is the past participle of the verb sold (or unsold).
The abstract noun is form of the verb to sell is the gerund, selling.
The word "sell" is also used informally as an abstract noun, for example a hard sell (aggressive persuasion), a soft sell (gentle persuasion), or a bit of a sell (lacking merit to be easily sold).
The abstract noun form of the adjective unique is uniqueness.
The abstract noun form for the adjective truthful is truthfulness.The word 'truthful' is the adjective form of the abstract noun truth.
The abstract noun for the adjective quick is quickness.
The abstract noun form of the adjective triumphant is triumph.
The word 'delightful' is the adjective form of the abstract noun delight.The abstract noun form of the adjective 'delightful' is delightfulnerss.
The abstract noun form of the adjective unique is uniqueness.
The abstract noun form for the adjective truthful is truthfulness.The word 'truthful' is the adjective form of the abstract noun truth.
The adjective for the abstract noun "famous" is "famous."
The abstract noun for the adjective quick is quickness.
The abstract noun for the adjective hot is hotness.
The abstract noun for the adjective "humble" is humility. Humility refers to the quality or state of being humble, modest, or respectful.
The abstract noun form of the adjective triumphant is triumph.
The word 'delightful' is the adjective form of the abstract noun delight.The abstract noun form of the adjective 'delightful' is delightfulnerss.
The abstract noun form of the adjective 'useful' is usefulness.The word 'useful' is the adjective form of the abstract noun use.
The abstract noun for the adjective famous is famousness.The word 'famous' is the adjective form of the abstract noun fame.
The abstract noun form of the adjective 'opinionated' is opinionatedness.The word 'opinionated' is the adjective form of the abstract noun opinion.
Weak is an adjective, and the related abstract noun is weakness. Weariness is an abstract noun (the adjective is weary).