BDAG glosses as "quite empty", but its usage in Hermas Mandates 5.2.1 is what got me:

"Now hear", he said, "how an angry temper works, how evil it is, and how it subverts God's servants by its working, and how it leads them astray from righteousness. But it does not lead astray those who are filled with faith, nor can it work on them, because the Lord's power is with them. But it can lead astray those who are empty-headed and double-minded.

Ἄκουε <νῦν>, φησί, τὴν ἐνέργειαν τῆς ὀξυχολίας, πῶς πονηρά ἐστι, καὶ πῶς τοὺς δούλους τοῦ θεοῦ καταστρέφει τῇ ἑαυτῆς ἐνεργείᾳ, καὶ πῶς ἀποπλανᾷ αὐτοὺς ἀπὸ τῆς δικαιοσύνης. οὐκ ἀποπλανᾷ δὲ τοὺς πλήρεις ὄντας ἐν τῇ πίστει, οὐδὲ ἐνεργῆσαι δύναται εἰς αὐτούς, ὅτι ἡ δύναμις τοῦ κυρίου41 μετʼ  αὐτῶν ἐστιν· ἀποπλανᾷ δὲ τοὺς ἀποκένους καὶ διψύχους ὄντας.

Note the "empty-headed" (translation from Holmes' 3rd edition) is tweaked for the context; the other usage in Hermas (Mandates 12.5.2) is translated "those who are empty".

This is a great word. I can see Jim West giddily using it in the proper context.