The noun diminution means the reduction of someone or something in size, intensity or importance.
Synonyms are lessening, decline, decay, or decrease.
The word origins from Anglo-French (13th century) diminuciun, Old French diminucion and directly from Latin diminutionem, earlier deminutionem, noun of action from past-participle stem of deminuere meaning “lessen, diminish”. It comes from de– meaning “completely” plus minuere meaning “make small”.
The diminution of that species is very evident.
There is a diminution in the supply of rice.
The diminution of the population led to a shortage of labor force.