According to CAED, "many" followed by a singular noun or pronoun is equivalent to "many" followed by the corresponding plural.

many a man tried = many men tried

So, many a____ is an adverb phrase used as an idiom.

That said, the examples cited above carry a difference of degrees.

Take this example:

I passed many a sleepless night tossing and turning but sleep did not visit me

In this example, the expression many a sleepless night selects each individual day included in the totality of one sleepless night after another and makes you realize how poignant my suffering was, which, I am sure, many sleepless nights would certainly fail to evoke.

The expression many a ___ is more like an oxymoron, a figure of speech that juxtaposes elements that appear to be contrary in one phrase to create a verbally puzzling yet engaging effect to drive home the message.

Other examples:

• same difference

• small crowd

• only choice

In my view, different from the traditional view, "many" in "many a man" and "many men" are different words, i.e. they have different origin.

"Many" in "many men" is related to German Menge (multitude).

"many" in "many a man" is related to "mancher Mann/manch ein Mann". The meaning of "manch" is approximately "more than a couple".

Probably "Menge" and "manch" belong somehow to the same word family. But "manch" is connected with singular and "Menge" with plural (eine Menge Bücher, a great many books). Astonishing that in English it is the same, though the two expressions use the same word many.

I know that there are members who don't like when I draw parallels to German. But I see no other way when I want to give a reason for the problem (many a + singular, many + plural). When you read etymonline you see that this problem is not clarified because many is explained as one word (related to manch) and not as two words ( related to manch and Menge).

This is definitely an odd construct.

• "Many men" refers to all men that have died at sea as a single group, thus the plural usage.
• "Many a man" refers to a group of individual events (a single man dying at sea).

The first focuses on the people, the second on the events.

Many a man couples with a singular verb because it indeed means "many of such men" which imparts singularity of every member of such group to denot effect and emphasis, whereas in "many men" there is no distinction among individuals; hence, plural verb. (alireza ameri, from Iran)

This phrase 'Many a man' epitomises the beauty, grace and peculiarity of English language. Singular usage puts emphasis on every individual in the group. And sometimes, beauty and elegance is better than logic.

''Many a'' is a determiner called as Quantifier. It denotes a singular noun. It means: being one of a large but indefinite number

many a man many another student

While as many as another Quantifier denotes more than one.