The speaker who has no specific words in his working vocabulary may be unable to explain or describe in a way that can be understood by his listeners.

在这个句子中，explain or describe 都是 the speaker 的动作，都需要接宾语（即：his meanings）。其实，who has no specific words in his working vocabulary，表面上是定语从句，实则是条件状语从句。意思是：如果说话者在行业词汇中没有特定的词，那么，他就无法用听众能理解的方式来解释或描述（他的意思）。

按照语法规则，这种省略是不可以的。