φθίω there is no diff. of sense in Act. and Pass.
I.to decay, wane, dwindle, of Time, πρίν κεν νὺξ φθῖτο (aor2 pass. opt.) first would the night be come to an end, Od.; so, τῆς νῦν φθιμένης νυκτός Soph.; φθίνουσιν νύκτες τε καὶ ἤματα they wane or pass away, Od.; μηδέ σοι αἰὼν φθινέτω let not thy life be wasted, id=Od.:— so, in the monthly reckoning, μηνῶν φθινόντων in the moon's wane, i. e. towards the month's end, id=Od.:— μὴν φθίνων the ending of the month, v. ἵστημι B. III. 3.
2.of the stars, to decline, set, Aesch.