Whereas 'freemasonry' itself is probably best rendered by 'sodalitas'.

At Rome, a 'sodalicius' (orig. an adj. meaning 'relating to companionship or fellowship', was a member of a society, often secret and not always legal (depending on the attitude of the government at the time), in which workers of the Roman lower classes--in some this included even slaves--banded together for worship of some specific deity or deities, and mutual financial and other assistance, especially for common meals and to ensure that all members enjoyed a decent burial.

The society's purposes, however, were not primarily political, although this was always a fear of the ruling authority under both the Repbulic and the Empire, and laws were accordingly passed to control these societies (notably the 'lex Licinia', passed sometime in the 2nd half of the 2nd cent. BCE). It was primarily a social and religious institution.

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Note added at 2004-03-03 23:44:46 (GMT)
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A neut. sing. substantive form \'sodalicium\' occurs in Cicero; the collective plur. \'sodalicii\' is more common under the Empire.