what are lemmas, please?

Lemmas (also, lemmata) are the form of word chosen to head a diction (also lexical) entry. For some languages this is fairly simple, e.g., in English, if it's a noun then use the singular form, and if it's a verb use the bare stem 9or infinite without to preposed). For languages that have a bit more inflection to them, you have to arbitrarily choose one of a word's many forms to use as the headword (or lemma). In Latin dictionaries, a verb is listed by its first person singular present indicative form, e.g., amo for 'to love'. (Literally the form means 'I love'.) For 'to be', one would look under sum. (And the infinitive of both those verbs are amare and esse respectively. Each language has a different tradition.

Oh, and dilemma is in fact two lemmata ( a lemma being a 'proposition' in Greek, from the verb lambano 'to take'.

Ceci n'est pas un seing.