terminologist
Concise Oxford English Dictionary © 2008 Oxford University Press:
terminology/tɜːmɪˈnɒləʤi/
▶noun (pl. terminologies) the body of terms used in a subject of study, profession, etc.
– derivatives
terminological adjective,
terminologically adverb,
terminologist noun.
terminological adjective,
terminologically adverb,
terminologist noun.
– origin C19: from Ger. Terminologie, from med. L. terminus ‘term’.
'terminologist' also found in these Oxford entries:

