noun
Common word for earwax. The cross-referenced 耳垢 (みみあか) is a synonym.
See also: 耳垢
耳かすがたまっているので、耳掃除をしよう。
Earwax has built up, so I'll clean my ears.
Synonym for earwax. 耳かす is more colloquial, while 耳垢 is slightly more formal or medical.
Compound of 耳 (ear) and かす (dregs, lees). The exact derivation of かす is uncertain, but it likely refers to residue or waste matter.