dirty
穢 centers on impurity and filth in a broad sense: something physically dirty, morally defiled, or spiritually unclean.
this impure world (as opposed to the pure land)
abhorrence of (living in) this impure world
night soil
person who gathers night soil
pure; clean; untouched; innocent
eta; group comprising the lowest rank of Japan's Edo-period caste system and whose work usually involved handling human bodies or animal carcasses
defiled body; unenlightened person's body
uncleanliness from contact with death, pregnancy, menstruation, etc.
ugly and filthy
various impurities (illness, menstruation, death, etc.)
穢 combines 禾 (grain) with 歲, which likely contributes the sound and carries a sense of overgrowth or impurity. The exact historical development is uncertain, but the character is associated with dirtiness or defilement.
Grain 禾 beside the complex 歲 suggests crops overgrown with weeds or spoiled by age, making them dirty and impure.
For アイ, imagine an eye (アイ) that sees only dirt and impurity everywhere: the eye -> アイ, and the dirty grain 穢 is all it can focus on.