Which word is a Tier 2 word appropriate for third grade?

The term "ordinal" refers specifically to a mathematical concept related to the order of numbers, which may not be commonly encountered by third graders in everyday language. While it is an important term in mathematics, its specialized nature limits its applicability across different contexts, making it less fitting as a Tier 2 word for this age group.

"Vertex" is a term used primarily in geometry to describe a point where two lines meet. Although it is an important concept in math, it is relatively specialized and not frequently used outside of mathematical contexts, which restricts its relevance for third graders in general vocabulary development.

While "bacteria" is a scientifically significant term, it may not be part of the everyday vocabulary for third graders. Its specific biological meaning might create barriers to understanding for younger students, thus making it less appropriate as a Tier 2 word that promotes broad vocabulary use across different subjects.