Green’s Dictionary of Slang

straightforwardly, candidly.

1893		Chevalier & Jones [perf. Albert Chevalier] ‘The Candid Man’ 🎵 Some likes a ’onest man who not only will, but can / Say wot ’e means and say it plain and plump.
1916		A. Brazil Luckiest Girl in School 237: ‘Miss Goodson doesn’t tell me plump out that I’ll be plucked, but I can see she thinks so!’.