撲空

lit. to rush at thin air / fig. to miss one's aim / to have nothing to show for one's troubles

to throw oneself at / to pounce on / to devote one's energies / to flap / to flutter / to dab / to pat / to bend over

empty / air / sky / in vain

to empty / vacant / unoccupied / space / leisure / free time

topological space (math.)