Hantzsch–Widman name

https://doi.org/10.1351/goldbook.H02737
A name for a heteromonocyclic @P04405@ having no more than ten ring members formed by the citation of 'a' prefixes denoting the heteroatoms followed by an ending (the 'stem') defining the size of the ring.
Source:
Blue Book Guide, p. 14 [Terms] [Book]