The word

Each of the following sets of letters can be made into a real word by adding three letters to the beginning, and the same three letters in the same order to the end.

For example, ANGLEM can have ENT added at the start and the end to become ENT + ANGLEM + ENT = ENTANGLEMENT.

ERTAINM
ISCOVE
ROW
IOXID
ROCOS

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Answer:

ENT + ERTAINM + ENT = ENTERTAINMENT

RED + ISCOVE  + RED = REDISCOVERED

ING + ROW     + ING = INGROWING

ANT + IOXID   + ANT = ANTIOXIDANT

MIC + ROCOS   + MIC = MICROCOSMIC