Green’s Dictionary of Slang

moo n.1

[SE moo, strengthened by abbr. moo-cow n.]

1. a woman, esp. a foolish one; often as silly old moo.

[UK]J. Ware Passing Eng. of the Victorian Era.
[UK]J. Speight ‘I Can Give it Up Anytime I Like’ Till Death Us Do Part [TV script] Silly bloody moo!
[UK]J. Speight ‘The Bird Fancier’ Till Death Us Do Part [TV script] It’s a rebate – you silly moo.
[UK]J. McDonald Dict. of Obscenity etc. 31: The now well-known phrase ‘silly old moo,’ [...] in the programme ‘Till Death Us Do Part’ [BBC 1960s+].
[UK]D. Mitchell Black Swan Green 127: Julia’s snaffled all the Jaffa Cakes [...] Greedy moo.

2. (US) as products of the moo-cow n.

(a) a beefsteak.

[US]Day Book (Chicago) 8 Sept. 17/1: ‘I want a rump steak, rare,’ orders another man. ‘Slab of moo — let him chew it!’ the waiter calls.
[as cite 1916].
[US]H.W. Bentley ‘Linguistic Concoctions of the Soda Jerker’ in AS XI:1 45: SLAB OF MOO – LET HIM CHEW IT. Rare rump steak.
[US]De Vries & Bushkin ‘Boogie Woogie Blue Plate’ 🎵 You can hear her calling orders like this [...] ‘Coming through with a slab of moo’.

(b) milk or cream.

[US]Wentworth & Flexner DAS.

3. see moo-cow n.