A servant who works between two others, or assists both.(noun)
A between-maid, or maidservant who helps the cook as well as the housemaid.(noun)
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Use "tweeny" in a sentence
""The original idea of the netbook was this would be the 'tweeny' -- in between a mobile phone and a laptop."
"If I never have to open another pink and yellow and leapard print and sequined jewelry box and hear that it's "tweeny" I will be so happy."
"The "tweeny" develops into housemaid or cook; the young girls employed in superior shops to wait on the elder shopwomen hope to develop into their successors, and the girls who nurse babies on the doorsteps are, after all, acquiring knowledge and dexterity that may fit them for domestic service or for the management of their own families a few years later."