when one twin envies another, particularly when one twin tends to excel in mutually competitive activities, or when one twin sees the other twin as more "successful" in life.
Chris had a raging case of twinvy when his twin brother Frank, the accomplished and eligible airline pilot, recently conceived triplets just a month after Chris could only muster an only child.
Noun;Verb. When one twin is envious of the other twins perceived success or ability.
Chris had a bad case of twinvy because his brother Sal was so successful.