A cognate object is the object of a sentence which repeats the verb (in noun form of course). Examples of what are sometimes considered cognate objects are:
1) He sang a song.
2) She danced a dance.
3) I drank a drink.
In these sentences the verb and the noun, which is the object of the sentence, are both, as it were, saying the same thing.
The term "cognate object" sometimes also refers to an object which has, more or less, the same meaning as the verb:
4) We ran a race.
5) They fought a battle.
6) He cried tears.
In all the above sentences, we can add an adjective before the nouns, like this:
7) She sang a beautiful song.
8) I drank a cold drink.
9) They fought a fierce battle.
10) He cried bitter tears.
However, there are some nouns which are related to verbs which are different in the grammar from the above. Here are some examples:
sleep > a sleep
laugh > a laugh
live > a life
die > a death
The relationship between "sleep" and "a sleep", "laugh" and "a laugh", etc. is different from the relationship between "sing" and "a song", "fight" and "a battle", etc.
The reason for this is that "a sleep", "a laugh", etc. are examples of true cognate objects. On the other hand, "a song", "a dance", etc. are not examples of true cognate objects.
In the next Column, I will discuss how the grammar of these two groups is different.
what are considered A：A（複数）と見なされるもの＜consider B A：BをAとみなす
as it were：ところが実際は
refer to ～：～を示す、表す
more or less：多少、ある程度