the plural of day is days.

the reason is that day does not stress closed syllables, so it is not necessary to change y into I plus es, but to add s directly.

day, when used as a noun, means "one day; Period; Day, name; (English, French and Spanish) Dai; (yue) Dai; (Arabic, Turkish) Dai ",when used as an adjective, means" daytime; Day by day ",when used as an adverb, means" every day; Often in the daytime. "

There are two cases in which the rules change in the plural form of English:

The first case is to add an s directly at the end of a word.

second, adding es at the end of words, specifically including:

1, ch,sh,s,x words.

2. words ending in "consonant letter +o".

3. Change Y into I and then add es with "consonant letter +y".

4. if the word ends in f and Fe, first change f and Fe into v and then add es.