A possible word is necessarily a possible syllable, though not the other way round. So TEA, as the first syllable of teacher, is not just a possible word, but a real one. But TI as the first syllable of Timothy is only a syllable and not a possible word.
Just as simply and obviously, a syllable with a short vowel and a final consonant like jam, mud, cut and run are also words.
But if it is obvious what might be a word, it is much less obvious what a word is.
A simple thought experiment. A says to B: “Do not do that!” B responds “What was the first word you said?” To which, the simple and obvious answer is “Do”. A might follow with: “But don’t!” To which B responds: “What was the last word you said?” Now A has again only one simple and obvious answer, “Don’t.” Although don’t represents a contraction of do and not, to answer “Not” would be at best perverse. And to try and say N’T would be no answer at all. The process of contraction has formed one word out of two. So how many words does this represent?
A similar question arises with broke. It is obviously related to break as the past tense form of the verb, where the same form is commonly used other than as a verb, as in “Take a break”, where what is to be broken is typically some everyday routine. On this basis, broke seems to contain two elements, what is known as a ‘stem’ and a past tense element – in this case, two ‘morphemes’.
What may be a problem for some first language learners is to distinguish between these things. Words often signal their identity as words by adding syllables, as in tummy, bottle, potato, spaghetti. But the fact that this is by a different sort of process from the complexification of the syllable by adding elements on the left or rigbt, as in stop or jump, is something which has to be learnt. For most children most of the time, this is not problematic. There are clues in the fact that stop and jump are commonly heard as stopped, or stops, or jumping. But for some children these clues are not enough.
More diagnostically, the fact that the final syllable of bottle is part of the word may be missed – wxigth the effect that it is said as BOT – or as BOP with the lip articulation of the B copied into what becomes the final sound. The normally developing child is highly sensitive to the unstressed second syllable, as one of the special characters of target language. Not noticing this may be part of a problem.
More gewnerally, the non-obviousness of what a word is is plainly a problem for the first language learner.