The Collaborative International Dictionary
Hygroscopic
Hygroscopic \Hy`gro*scop"ic\, a. [Cf. F. hygroscopique.]
Of or pertaining to, or indicated by, the hygroscope; not readily manifest to the senses, but capable of detection by the hygroscope; as, glass is often covered with a film of hygroscopic moisture.
Having the property of readily inbibing moisture from the atmosphere, or of the becoming coated with a thin film of moisture, as glass, etc.
Douglas Harper's Etymology Dictionary
Wiktionary
hygroscopic
a. (context physics chemistry English) Readily taking up and retaining water, especially from the atmosphere.
WordNet
hygroscopic
adj. absorbing moisture (as from the air)
Usage examples of "hygroscopic".
It should be ignited and cooled out of contact with air just before using, since it is hygroscopic.