AnonymousI couldn't find this word in any dictionaries.
I couldn't find this word in any dictionary.
Is there any difference between the two sentences?
If there isn't any difference, which is the best choice?
Both are grammatical. The singular is better (more idiomatic), in my opinion. Unfortunately, it is difficult to capture the conditions under which the singular (or plural) is most suitable. Here, for example, you looked into each dictionary,
one at a time, so singular seems more appropriate. Further, once you find the word in
one dictionary, presumably your search is done; in this case the singular again seems more appropriate. This is not a grammatical explanation, of course, but a situational one, and I'm afraid that the choice is usually made on the basis of situations rather than on rules.
AnonymousI have just closed my dictionary (or perhaps just a few minutes ago), which form should I use between the following ones?
I couldn't find this word...
I wasn't able to find this word...
I haven't been able to find this word...
Use
I couldn't find this word. wasn't able to is OK too.
But if you did find it, use I was able to find ... -- not I could find .... could alone cannot convey the idea of having succeeded, while, in seeming contradiction, could not alone can convey the idea of having failed!
CJ