Lock-keeper’s slow decline (5)

I believe the answer is:

slide

I believe this clue is a double definition.

'lock-keeper's' is the first definition.
(mechanical term)

'slow decline' is the second definition.

(Other definitions for slide that I've seen before include "Slip, slither, skid" , "Microscope glass" , "Playground equipment with sloping surface" , "Playground chute" , "Make mild fun of" .)

I've seen this clue in The Times.

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