For , we get the maximal abelian extension by adjoining all roots of unity, i.e., taking compositum of all -th cyclotomic fields (this is the famous Kronecker-Weber theorem).
2005, T. Y. Lam, Introduction to Quadratic Forms over Fields, American Mathematical Society, page 333:
compositumn (genitivecompositī); second declension
that which is agreed; an agreement, compact, etc.
Synonyms:condiciō, stipulātiō, pactum
compound word, compound
使用する際の注意点
This noun also appears (in the ablative only) in the phrases ēxcompositō(“according to agreement”, “by agreement”, “in concert”) and dēcompositō(“by agreement”), as well as more rarely (in the same sense) alone as compositō.