Green’s Dictionary of Slang

garret n.

1. [late 18C–1930s] the head (cf. upper storey under upper adj.).

2. [early 19C–1930s] (UK Und.) the fob pocket.

3. [late 19C] the mouth.

4. [late 19C+] a woman’s handbag.

In phrases

abroad in the garret (adj.)

[early 19C] dazed.

have a rat in the garret (v.)

[2000s] (N.Z.) to act eccentrically.

shut up one’s garret (v.)

[late 19C] to be quiet, to stop talking.