Whatchamacallit
It is derived from the phrase "what-you-may-call-it"
what you -> 口語讀成 whatcha
may -> 口語讀成（弱化）/muh/
call it -> 口語連讀成 callit
---> whatchamacallit
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Etymology of the English word thingamajigger
the English word thingamajig
derived from the Obsolete English word jig
derived from the Obsolete English word thingum
http://www.myetymology.com/english/thingamajig.html:
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What the hellja do that for?
Wuddaya want the light for?
Listen, I toleja about that ... blah blah ...
