What does waiting/clock icon next to a message mean and what if I delete message in this state? When my device is not connected to any network (WiFi/Cellular data) and I send any message, I have seen a waiting/clock icon next to that message.

So what exactly does that mean? Is that message added to a queue for next batch process to inform server or something else?

And during that state (waiting/clock icon next to message) if I delete that message, will that deleted message still be delivered to the recipient?

Actually, I mistakenly sent a message to one of my contacts and luckily that time I was not connected to any network. After a few seconds when I realized this, I deleted that message. But I am not sure if it got deleted completely or it will get delivered when I reconnect to any network. I don't want that message to be delivered to the recipient, so I had disabled all networks on my device.
The Clock icon means that you haven't sent the message yet. If you see a single tick mark it means that you have sent the message and it has been received by the WhatsApp server(but not the destined user)
If you see a double tick mark, that means the message has been received by the recipient too.

If a message has a single tick with it, it can't be stopped from getting to the user. But if you sent a message when offline and deleted when the phone was offline I don't think the message will reach its destination.