1.Definition: (physics) of waves having a constant phase relation

2.Definition: capable of thinking and expressing yourself in a clear and consistent manner

"She was more coherent than she had been just after the accident"

Related Adjective(s):logical, lucid

3.Definition: marked by an orderly, logical, and aesthetically consistent relation of parts

"A coherent argument"

Related Adjective(s):consistent, logical, ordered

4.Definition: sticking together

"Two coherent sheets"

Related Adjective(s):tenacious