unspeechfuladj.
Etymology: Previous versions of the OED give the stress as: unˈspeechful.
the mind > language > speech > taciturnity or reticence > [adjective] > lacking words for expression
1853 F. W. Faber (1854) 365 Lighting up their land of pain and unspeechful expectation.
This entry has not yet been fully updated (first published 1926; most recently modified version published online June 2019).