orthohelium
/ˌɔːθəʊˈhiːlɪəm/ /ˈɔːθəʊhiːlɪəm/Physics
noun
The form of helium whose spectrum exhibits a fine structure of triplets owing to the spins of the two orbital electrons being parallel.
Origin
1920s. From Danish orthohelium from ortho- ortho- + helium helium. Coined as an antonym of the earlier parhelium.