I just saw the following at English language learners stack exchange meta forum (ELU meta).

• We should not be pasting definitions from online dictionaries into answers when their terms of service prohibit such use

As one of the answers there suggests, it may make sense theoretically, but I'm wondering if it really does even theoretically.

My naive understanding is that as long as you are clear about its sources, and the quoted amount is decent, there can't be an issue (the amount may be problematic in general, but in case of ELU, usually less than dozen definitions per answer).

Now my questions are

• Specifically about copy-pasting dictionary definitions on ELU answers, can it be a legal issue even theoretically?

• Does the collective nature of web forum make difference? For example, if it can be an issue on SE, does that mean copy-pasting a word definition on my blog post would also be a problem?

• In general is it possible to legally forbid any amount of copy-paste from a website, assuming the texts are clearly presented as citation?

Regionally I restrict the question to the US, if it matters.

I just saw the following at the English language and usage stack exchange meta forum (ELU meta).

• We should not be pasting definitions from online dictionaries into answers when their terms of service prohibit such use

As one of the answers there suggests, it may make sense theoretically, but I'm wondering if it really does even theoretically.

My naive understanding is that as long as you are clear about its sources, and the quoted amount is decent, there can't be an issue (the amount may be problematic in general, but in case of ELU, usually less than dozen definitions per answer).

Now my questions are

• Specifically about copy-pasting dictionary definitions on ELU answers, can it be a legal issue even theoretically?

• Does the collective nature of web forum make difference? For example, if it can be an issue on stack exchange (SE), does that mean copy-pasting a word definition on my blog post would also be a problem?

• In general is it possible to legally forbid any amount of copy-paste from a website, assuming the texts are clearly presented as citation?

Regionally I restrict the question to the US, if it matters.

I just saw the following at ELU meta.

• We should not be pasting definitions from online dictionaries into answers when their terms of service prohibit such use

As one of the answers there suggests, it may make sense theoretically, but I'm wondering if it really does even theoretically.

My naive understanding is that as long as you are clear about its sources, and the quoted amount is decent, there can't be an issue (the amount may be problematic in general, but in case of ELU, usually less than dozen definitions per answer).

Now my questions are

• Specifically about copy-pasting dictionary definitions on ELU answers, can it be a legal issue even theoretically?

• Does the collective nature of web forum make difference? For example, if it can be an issue on SE, does that mean copy-pasting a word definition on my blog post would also be a problem?

• In general is it possible to legally forbid any amount of copy-paste from a website, assuming the texts are clearly presented as citation?

Regionally I restrict the question to the US, if it matters.

I just saw the following at English language learners stack exchange meta forum (ELU meta).

• We should not be pasting definitions from online dictionaries into answers when their terms of service prohibit such use

As one of the answers there suggests, it may make sense theoretically, but I'm wondering if it really does even theoretically.

My naive understanding is that as long as you are clear about its sources, and the quoted amount is decent, there can't be an issue (the amount may be problematic in general, but in case of ELU, usually less than dozen definitions per answer).

Now my questions are

• Specifically about copy-pasting dictionary definitions on ELU answers, can it be a legal issue even theoretically?

• Does the collective nature of web forum make difference? For example, if it can be an issue on SE, does that mean copy-pasting a word definition on my blog post would also be a problem?

• In general is it possible to legally forbid any amount of copy-paste from a website, assuming the texts are clearly presented as citation?

Regionally I restrict the question to the US, if it matters.