tribrach
Concise Oxford English Dictionary © 2008 Oxford University Press:
tribrach /ˈtrʌɪbrak, ˈtrɪ-/
▶noun Prosody a metrical foot of three short or unstressed syllables.
– derivatives
tribrachic /-ˈbrakɪk/ adjective.
tribrachic /-ˈbrakɪk/ adjective.
– origin C16: via L. from Gk tribrakhus, from tri- ‘three’ + brakhus ‘short’.
'tribrach' also found in these Oxford entries:

