Many thanks guys ! I agree it seems to ERUVIM although it appears not to be in Chambers 11th edition, which only lists ERUV.
Wikipedia and dictionary.com both state that ERUVIN is the plural of ERUV, just to confuse things further. However, a Google search reveals lots of ERUVIM around the world.
I remain somewhat confused but relieved to have finished 2577 !
Cheers,
Alan