陰イオン is read as いんいおん (inion) and means anion.
いんいおん
inion
いんよう
cosmic dual forces
いんき
spirit of yin
いんせい
negative (result)
かげぐち
malicious gossip
かげ
gloom (in someone's expression, nature, etc.)
いんぼう
conspiracy
かげり
shadow (e.g. on someone's happiness)
いんえい
nuance
いんしつ
shady and damp
いんせいはんのう
negative reaction (in patient)
いんせいだい
Cryptozoic (period)
かげひなた
double-faced