I agree with Reme: it's more useful if you give them the definition of the word and an example to clarify the meaning, only when the students' level is high enough to understand what you are trying to explain to them. Of course, this is not useful for children or beginners levels, where I found that they can be frustrated when they don't understand a word of the definition. But, little by little, with easy or specific words in a context they start to understand your definitions.
This is my opinion