- (in the plural) The relationship between two cousins or two groups of cousins whose parents are brother and sister, respectively, these parents should be of the same nuclear family .
- Many societies forbid marriage between parallel cousins, but encourage marriage between cross-cousins or second cross-cousins.
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Cross-cousins are normally just called "cousins", unless there is need to disambiguate from parallel cousins.
In anthropology, a patrilineal or patrilateral cross-cousin is a cousin born to one's paternal aunt; a matrilineal or matrilateral cross-cousin is a cousin born to one's maternal uncle; and a bilateral cross-cousin is both, as his/her parents are co-siblings-in-law to one's own parents. (However, bilateral cross-cousin marriage is defined differently, as the custom where either patrilateral or matrilateral marriage is acceptable, in opposition to unilateral cross-cousin marriage.)
When it comes to second or third cousins, the difference between cross and parallel depends on the society. In Tamil, which is typical, cross-cousins are those for which the intermediary relations include an odd number of gender switches. Those for which there is an even number (including zero), are parallel, and are counted as siblings. That is, two cross relationships cancel out.