relating to the country (outside of towns and cities, and low population areas), country people or life, or agriculture. (source #5)

of, relating to, characteristic of, or constituting a city. (source #5)

Microscopic, plant-like marine organisms (mostly algae and diatoms), which are responsible for most of the photosynthetic activity in the oceans. Phytoplankton are the base of the ocean food web, and they absorb about as much carbon dioxide from the atmosphere each year as plants on land do. (Source #2)