Green’s Dictionary of Slang

lay (up) in lavender v.

[ironic use of SE lay up in lavender, to put aside carefully for future use. Lavender was then, as now, kept with stored linen and other fabrics]

1. [late 16C–19C] (also lay) to pawn.

2. [17C–19C] to put out of harm’s way; to hide, e.g. from the police.

3. [17C–19C] to imprison.

4. [late 17C–19C] (also lie in lavender) to die.

In phrases

in lavender

1. in pawn.

2. [mid-17C; mid-19C–1930s] hidden from the police.

3. [late 18C] in a charity hospital.

4. [1930s] (US Und.) dead.