The issue is that there is no concept of a word for the speech recognition engine until it has already found a hypothesis. Until it has searched for a hypothesis, it is just dealing with a set of phonemes in the utterance that it found, and the utterance is defined by speech followed by a pause. After it attempts to recognize the utterance, there is a concept of a word because the phonemes in the utterance were matched with words with a high probability of being the spoken words. So concepts like “one word” would have to come into effect after the speech utterance has been analyzed by the engine, not before.
What you could do if you only want to know the first word a user said is to take the delivered hypothesis (either in OpenEars or RapidEars) and split it into an array along the whitespace separator and then just use the word at index zero.