"Astrolabe," "audiometer," "death" and "ambidextrous" are examples of unusual words on a fifth-grade vocabulary list. Fifth-grade vocabulary lists include some unusual words because they pertain to fifth-grade academic subjects; other words on these vocabulary lists occur frequently in reading and writing.
While most fifth-grade vocabulary words are sight words – easily recognizable, high-frequency words – some of them pertain to a specific academic subject. Though a fifth-grade student might not need to know technical jargon to be considered literate, familiarity with certain terms helps in other academic areas. "Astrolabe," for example, is not a sight word, but it is a term that a student might encounter in a fifth-grade science class. The same is true for "audiometer."
"Ambidextrous," on the other hand, is not a technical or scientific term, but it poses a spelling challenge. The goal of many vocabulary lists is to develop word recognition as well as spelling competency. Fifth-grade vocabulary lists that expose students to unusual words typically help them achieve a higher level of reading comprehension in the future.
Some of the unusual words on a fifth-grade vocabulary list come from the Fry sight words. This list contains many of the most common words for reading and writing. While "death" isn't part of the fifth-grade curriculum, it is still a term that occurs frequently in English reading and writing.