Hodor from Game of Thrones manifests a condition called Broca's aphasia. Here's a real-life example of a man who communicates only using the word "tono."

According to the American Speech-Language-Hearing Association, Broca's aphasia is

A type of nonfluent aphasia, so called because speech production is halting and effortful. Damage is typically in the anterior portion of the left hemisphere. The dominant feature is agrammatism (impaired syntax). Content words (nouns, verbs) may be preserved but sentences are difficult to produce due to the problems with grammar, resulting in "telegraphic speech." In its more severe form, spoken utterances may be reduced to single words. Comprehension is typically only mildly to moderately impaired, and impairments are primarily due to difficulty understanding complex grammar. Repetition of words and sentences is usually poor.

Here's a Hodor supercut for those interested: