- salty; saline
- of, or relating to the degree of saltiness
Haline is part of the compound word thermohaline, meaning "regarding temperature and salinity." Thermohaline in turn is most commonly used in the phrase "thermohaline circulation" which is an ocean current caused by temperature and salinity differences between masses of water. It would be nice if "saline," "thermosaline," and "thermosaline current" were simply used instead, but of the three only "saline" commonly is.
Why "h" and not "s"? The word probably has roots in the Greek "halinos," meaning "of salt." G. Kharimanis notes that:
#there is a rule that the initial `s' of Indoeuropean words is converted into an `h' in the corresponding Greek;
#The Greek "halas" (root: halat-) salt, and hals (root: hal-) sea (aka thalassa).
Haline is a more general sense of 'saltyness'. It may come from halides dissolved in water; for sodium chloride you can say saline; for a potassium iodide (a different halide) haline could be more technically correct.