Sull’origine dello spagnolo añadir

The origin of the Spanish word añadir is to be sought in the Vulgar Latin
*ĭnnaddĕre (ĭn + addĕre). The cause of the geminate -n- has been explained in
several ways. The hypothesis which has received the greatest attention has
been advanced by Joan Corominas, who attributes the supposed ĭnnaddĕre
to a reanalysis process. The most likely explanation, however, is that the
lengthening of the final -n- of the prefix could be explained in a pan-Romance
perspective. Several studies have demonstrated the existence, in ancient
and modern Italian and Romanian varieties, of a process of “doubling of
the final prevocalic consonant”. This phenomenon originally affected all
monosyllables and one-syllable prefixes ending in a consonant, whereas,
today, it takes place generally in a limited number of words. Evidence of a
final consonant doubling may also be found in the Gallo-Romance domain.
With regard to the Ibero-Romance varieties, it should be noted that the
doubling of the final -n- of the prefix is well attested in modern Catalan.
From these data one may infer that the doubling process was already present
in Late Latin or Proto-Romance. Such a theoretical framework provides a
coherent explanation of the Vulgar Latin *ĭnnaddĕre.