Early 19th century; earliest use found in ‘Robert Rabelais’ (fl. 1819). Apparently an extended form of thing or thingum; with the ending compare jigamaree and perhaps also -ery, -ary.
Definition of thingamerry in US English:
thingamerry
(also thingumary)
nounˈθɪŋəməri
rare, informal
Thingummy.
Origin
Early 19th century; earliest use found in ‘Robert Rabelais’ (fl. 1819). Apparently an extended form of thing or thingum; with the ending compare jigamaree and perhaps also -ery, -ary.