noun

1. a turning or being turned the opposite way; reversal
2. a reverting, or returning, as to a former state, custom, or belief
3. Biol.
   1. a return to a former or primitive type; atavism
   2. the return, or reappearance, of characteristics present in early ancestral generations but not in those that have intervened
   3. an individual or organism with such characteristics
4. Law
   1. the right of succession, future possession, or enjoyment
   2. the return of an estate to the grantor or the grantor's heirs by operation of law after the period of grant is over
   3. an estate so returning

Etymology: ME < MFr < L reversio < reversus: see reverse