Right, so what's the correct expression, wise up or wisen up, or both? And in the past, is it wised or wisened?

Present = wise up. eg Wise up, stupid!

Past = wised up. eg When he wised up, it was too late.

It's an informal and idiomatic expression. It is often used rudely.

Please say 'Please'. It makes the volunteers here feel happy. Thank you.

Veteran Member69,557
Moderator: A super-user who takes care of the forums. You have the ability to message a moderator privately should you wish. These users have a range of elevated privileges including the deletion, editing and movement of posts when needed.Teachers: Users in this role are certified teachers. This may include DELTA, CELTA, TESOL, TEFL qualified professionals. Email a scan of your qualification to an admin, if you wish to be considered.
Live chat
Registered users can join here