{ghoj} “learn” is obviously a root word. {ghojmoH} “teach” is obviously derivative, but since the English gloss is a different word, most people count it as a distinct word worth counting. Similarly, there’s {ghojwI’} “student, and {ghojmoHwI’} “teacher”, and while we’re at it, {ghojmoHwI’’a’} “professor”, thought that doesn’t count because it hasn’t made it into the lexicon, despite being pretty obvious.

I think "distinct word" is the wrong thing to be looking for. "Unit of meaning," maybe "lexeme," is more useful in Klingon. I think all the words you gave above are distinct words, whether or not they are lexemes, in the same way that run, ran, running, runs are all distinct words but not distinct lexemes.

The main reason we have words like ghojmoH in The Klingon Dictionary is because people would want to look up the word for teach in the English–Klingon side, and if the word appears in that side it would also appear in the Klingon–English side. In a top-notch translation dictionary I would expect the English–Klingon dictionary to only list English lookup words, and the Klingon-English dictionary to only list Klingon lookup words, but within the K-E lookups various important inflections with distinct English translations could be given. For instance:

ghoj learn
     ghojmoH teach; ghojwI' student

The implication would not be "These are all lexemes," but rather "This is a lexeme, and here are some derived forms that may correspond to distinct words in English that you might be looking for." You wouldn't see every possible inflection, just some significant ones, and there would be no implication intended that other inflections are less valuable.

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SuStel
http://trimboli.name