A single message is not harassment though.

You can't make that blanket statement.

A single punch is battery. A single genital grab is sexual assault. A single demand for quid pro quo sexual favors in exchange for professional rewards is sexual harassment. A single message asserting that an individual is not right for their job because of their gender creates a hostile work environment, and that's also sexual harassment.

Just because there can be cases where a single message does not constitute sexual harassment doesn't mean that a single message can never amount to sexual harassment.

A single event can be illegal, immoral, wrong, or any one of a bunch of other words, and a single event is never harassment because harassment requires multiple events.

A single demand for quid pro quo sexual favors in exchange for professional rewards is a sexual offence, a bad one, and alone it is not harassment. IANAL, though the dictionary definition sticks with me, especially the key words: "multiple", "unwanted", and "intentional".

That's why "harassment" as a word exists, it is to indicate that multiple unwanted events have happened intentionally.

Maybe the legal definition of "harassment" differs from the dictionary definition. If so, a new word for single event harassment needs to be chosen.

> A single demand for quid pro quo sexual favors in exchange for professional rewards is a sexual offence, a bad one, and alone it is not harassment.

That's simply wrong -- a single egregious instance can certainly constitute harassment, both in terms of common sense and in terms of legal consequences. What matters is severity -- and though repeating the behavior makes it more likely to be judged as severe, one bad incident can easily exceed the threshold. A quid-pro-quo proposal of sex-for-promotion is a perfect example.

But that's just a single instance, and by definition not harassment.

Unless my understanding of the word "multiple" (and "persistently" and "continually") is completely wrong...

Harassment does not require "multiple". That's just wrong.

The dictionary of definition DEFINITELY does. (Caps for emphasis, not yelling.)

It is not a requirement. Consider the Oxford English definition:

https://en.oxforddictionaries.com/definition/harassment

> Aggressive pressure or intimidation. ‘they face daily harassment and assault on the streets’

English doesn't have a definitive dictionary, anyway -- usage determines meaning. It has been the case for decades that a single quid pro quo proposal could be ruled as "harassment" in court. (As it should be!) Is it any wonder that colloquial understanding would reflect legal reality?

Both the legal and linguistic standards for harassment do not require repeated events. You are incorrect.

If you're talking about the legal definition, that depends largely on your jurisdiction (there are many where a single instance does constitute harassment; perhaps most states in the US require a "culture"). Unfortunately again, common language and legal language overlap but with slightly different meanings.

However, in every case where multiple messages were sent, that's clearly harassment in many jurisdictions. Additionally, the sum of actions by multiple people constitutes harassment. Also many jurisdictions will consider it harassment if there is a single, severe incident. However, many of these laws only apply when a co-worker is the harasser.

In summation: your statement is not necessarily correct.

Somewhat depends on your point of view. A single message sent may not be intended as harassment, but receiving a single message from multiple people can certainly feel like harassment. An individual act might not be harassment, but it can definitely contribute to it.