agreement and pacification
The two other common names for celestial bodies are planets and moons. Planets are large objects that orbit around stars, while moons are natural satellites that orbit around planets.
The names of two common rhythmic patterns in poetry are anapest and iamb.
Two very common street names for opium are gee and goric. Opium has also been commonly called pen yan and ze.
If you are talking about temperature, the most common are Fahrenheit and Celsius, but there are other scales as well.
Depending on where you live, two other common names for a woodchuck are "ground hog" and "whistle pig".
It's a Pie graph or Pie Chart are two other common names for a circle graph.
Because the same common names are used to describe different plants... which may be similar to each other or wildly different. The scientific names of plants are specifically designed to identify a particular species clearly and unambiguously.
least common multiple, or LCM
IEEE 1394 and i.LINK. Two other names for "Firewire" are IEEE 1394 and i.LINK.
They are two names for the same thing.
Genes and chorosomes
There are dozens upon dozens of brand names for ibuprofen. The two most common are Motrin and Advil.