Green’s Dictionary of Slang

wide-oh! excl.

[wide adj. (1)]

look out! take care! be on your guard!

[UK] ‘’Arry on Woman Rights’ in Punch 2 Apr. 156/2: And now they’re [i.e. suffragettes] connivering rounder arter votes, I sez ‘Wide-oh’s’ th word, Or us men won’t be in it all.