haltere

/ˈhæltɪə/
noun (pl) halteres (hælˈtɪəriːz)
1.
one of a pair of short projections in dipterous insects that are modified hind wings, used for maintaining equilibrium during flight Also called balancer
Word Origin
C18: from Greek haltēres (plural) hand-held weights used as balancers or to give impetus in leaping, from hallesthai to leap