tj, rj,ej
The first two letters of the name, Argon.
Ox
so
Chemical symbols use one or two letters from the name of the element.
Headache and heartache begin and end with the letters he.
Og.
ai, ox
Kansas becomes Arkansas by adding two letters.
Rutabaga and cabbage
There are two types of whales that have only three letters in their name. The Fin whale and the Sei whale.
Claymore is the name of a sword.
E.t.