Green’s Dictionary of Slang

the tongue; ext. to firm speech as in ‘have one’s say’.

1857		‘Ducange Anglicus’ Vulgar Tongue.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl. 27: first of May. Say; in expressions like I’ll have my first of May when I get hold of him! (19th c.; still current).