Gismo functions in both directions, I say (6)

I believe the answer is:

doodah

'gismo' is the definition.

I cannot understand how the rest of the clue works.

(Other definitions for doodah that I've seen before include "Thingamy" , "one can't name" , "Whatchamacallit, thingamajig" , "thingumajig" , "Whatsit" .)

I've seen this clue in The Times.

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