σκῐᾱμᾰχ-έω · skiamach-eō — LSJ
fight against a shadow, i.e. an imaginary opponent, and so, spar, Posidon. 16 J., Plu. Sanit. 2.130e, Paus. 6.10.3: πρὸς τὸν οὐρανὸν σκιαμαχῶν sparring with the sky, ‘baying at the moon’, Cratin. 17 (lyr.).
metaph., Pl. Ap. 18d; πρὸς ἀλλήλους Id. R. 520c; πρὸς ἡμᾶς αὐτούς Id. Lg. 830c; πρὸς τὸν οὐκέτι ἐν ζῶσιν ὄντα Πλάτωνα ἐσκιαμάχει Numen. ap. Eus. PE 14.6:—Pass., ἔπη μάτην σκιαμαχούμενα thrown out at random in disputations, Luc. Pisc. 35.—σκιομαχέω is a later form in codd. of Ph. 1.356, Antyll. ap. Orib. 6.29.3.