from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Indicating coincidence of high tides or low tides.
- adj. Of or relating to a line that passes through each location on a coastal map where tides occur at the same time of day.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Describing the locations (and of related lines on a chart) linking places where tides occur at the same time of day
from the GNU version of the Collaborative International Dictionary of English
- adj. Marking an equality in the tides; having high tide at the same time.
from The Century Dictionary and Cyclopedia
- Marking an equality of tides.
co- + tidal (Wiktionary)
The diagram I show you is a rough chart of cotidal lines, which I made out of the information contained in _Whitaker's Almanac_.