[While] we're on the subject, I have to say~

During the time that; at the same time as

http://www.oxforddictionaries.com/us/definition/american_english/while

"while we're on the subject" is a set form of words.

Dear Park

"While" has its ordinary dictionary meaning here, which is something like "during the time". It's used in complex sentences in order to connect two situations which are happening around the same time. It's a word that should be learnt at elementary level, and worked on in more detail at intermediate level.

"While we're on the subject,..." is a common expression in spee

park sang joonWhile we're on the subject,

[Since / Given that] we are (already) talking about it/this, ...

CJ

While we're on the subject, I have to say that dinosaurs don't go "ruff."

I'm sorry for my belated question.
Then, I'd like to know if here "have to" means "must."

park sang joonI'd like to know if here "have to" means "must."

Yes, it does.

CJ