hemera (Greek #2250)
day, i.e. (literally) the time space between dawn and dark, or the whole 24 hours (but several days were usually reckoned by the Jews as inclusive of the parts of both extremes); figuratively, a period (always defined more or less clearly by the context)
KJV usage: age, + alway, (mid-)day (by day, (-ly)), + for ever, judgment, (day) time, while, years.
Pronounce: hay-mer'-ah
Origin: feminine (with 5610 implied) of a derivative of ἧμαι (to sit; akin to the base of 1476) meaning tame, i.e. gentle
aion (Greek #165)
properly, an age; by extension, perpetuity (also past); by implication, the world; specially (Jewish) a Messianic period (present or future)
KJV usage: age, course, eternal, (for) ever(-more), (n-)ever, (beginning of the , while the) world (began, without end). Compare 5550.
Pronounce: ahee-ohn'
Origin: from the same as 104