If the Kalahari students don't know a word that you cannot explain with a picture, then you have three basic choices. Firstly, you can give a definition. So if the new word is 'predict', you can explain that predict means saying what you think will happen in the future. Secondly, you can use the word in a sentence or two exemplifying it, as here with the word 'superstitious'. And thirdly, it may be best to simply give several examples of the word, because neither a definition nor an example sentence can easily convey the meaning; for example, the word 'preposition': 'in, on, at, by, with, under are all prepositions'. Of course, there is no reason why you should not combine methods to make sure you are really understood.
Before continuing, watch this video of a former Kalahari participant explaining the word 'sin'.
Ok, now it's time to try out these methods yourself. Here is a list of words from various practice exam papers that Kalahari students have used over the past few years. Pause the video and think about how you would explain each of these words using one of the methods we have discussed. The word 'heat' here is polysemous and has to do with athletics not with temperature.
Of course, it is entirely possible that Kalahari will still not understand the word after your long explanation. If that is the case, you should get a translation of the word in Tswana, either from one of the other students in your teaching group, or from a Kalahari teacher after class. In some cases you may want to skip a long explanation in English altogether and tell or show them the Tswana translation that you have learned in advance or that a more proficient student in the group tells you. This is perfectly fine on occasion, but in general it is better to try stick to English.