Columbia subject headings:
H (The sound)
Indo-European languages--Grammar, Historical.
Indo-European languages--Morphology.
Indo-European languages--Phonology, Historical.
Harvard subject headings:
H (The sound)
Indo-European languages--Grammar, Historical.
Indo-European languages--Morphology.
Indo-European languages--Phonology, Historical.
Princeton subject headings:
H (The sound)
Indo-European languages--Morphology.
Indo-European languages--Phonology.
Proto-Indo-European language--Morphology.
Proto-Indo-European language--Phonology.