Q:

Lexical diversification

What is the precise scientific name for the following phenomenon: 
Spanish: Los tios = aunt + uncle
English: aunt + uncle
There is no single expression in English which encompasses both the meaning of "aunt" and "uncle"
I have heard this is called "diversification", and the opposite is "neutralization" - is that right? Can anybody cite a source for that? 

A:

Since English does have terms jointly referring to certain couples of relatives, e.g., parents (of x), grandparents (of x), it could be claimed that the absence of a term jointly referring to 'an uncle of x and his wife' is a 'lexical gap' in English. That is the only technical term I am aware of to describe phenomena SIMILAR to the one you are interested in. However, that claim might also easily be challenged. For example, it could be argued that, in the English kinship system, terms jointly referring to couples of relatives of x exist (let's say) only when both members of the couple are related to x by relations of the same kind (say a blood relationship, rather than a in-law one). Both parents of x, and the four grandparents of x are related to x by (1st/2nd degree) consanguinity, but in the case of the couple formed by an uncle of x and his wife (or an aunt of x and her husband), that condition is not satisfied, and, as a consequence, in English, there would arguably be no reason to expect a single term jointly referring to an uncle of x and his wife. Spanish, of course, would simply be different from English at this point, say in that such a difference between blood and in-law relationships does not prevent the existence of terms jointly referring to such couples as those constituted by an uncle/cousin/nephew... of x and their wives (or an aunt/niece... of x and their husbands, or whatever civil or de facto relationship might be relevant). [That's just an idea that occurs to me by way of illustration; I have not really looked in depth at the kinship terminology of either English or Spanish]. To really determine all the factors that count in this respect, one would have to check how other kinship and non-kinship terms (e.g., "friends", "neighbours",...) behave. Of course, as soon as you started comparing the lexicons of many different languages and attempted to define a sort of 'panlinguistic lexicon' (a multidimensional logical space allowing for all lexical items possible in all languages), such apparent or real 'lexical gaps' would proliferate enormously, and you would have to decide what and what not you want to consider a 'lexical gap'.

