Lexical polarization is used in this paper as a convenient label for the influence exerted by one word on its semantic opposite. In Classical Latin, for instance, DEXTER serves for ‘right’ and SINISTER for ‘left’. The ancient Romance expressions for ‘right’ are traceable to DEXTRU (to the extent to which DĪRĒCTU ‘straight’ or another rival word has not usurped its place), yet Romance equivalents of ‘left’, barring innovations, consistently presuppose the scantily documented late variant SINEXTRU rather than common SINISTRU (which alone is found even in the glosses). Taking into account the pronunciation of Late Latin, we may reckon with the presence of the pair DESTRU ˜ SINESTRU (SENESTRU) on the colloquial level prior to the disintegration of the Empire. The anomaly in the development of sinistru is thus reduced to the excessive opening of its stressed vowel, which was in any event bound to open to a minor extent: the i advanced not only to [e], as in comparable words, but to [ε]. This departure from the norm, in the absence of other clues, is most plausibly accounted for by assuming a certain amount of pressure exerted by [destru] on [senestru], until the two words reached the maximum degree of similarity compatible with the maintenance of their basic difference. We are here concerned with an instance of formal attraction through association by contrast, a process in which a weaker (passive) partner is reshaped on the pattern of its stronger (active) opposite.