Green’s Dictionary of Slang

1. (US) a ‘flighty’ young woman.

1889		Nat. Police Gaz. (NY) 23 Nov. 10/1: [C]herry lipped, rosy cheeked suspender bursting, suicide inducing , palpitating , pulsating glddles.
1890		Nat. Police Gaz. (NY) 22 Feb. 2/1: Two Bristol, Conn., giddies, recently tackled those lung-destroying articles [i.e. cigarettes] and came near burning a hotel and landing themselves in the Promised Land. Fie, girls! for shame!

2. (Aus.) a womanizer, a lothario [? play on giddy goat/goat n.¹ (1)].

1906

E. Dyson Factory ’Ands 130: ‘Levi’s a giddy... He’s a rake, a bloomin’ Henry the Eighth’.

3. see giddy gout n.