Abarim Publications' online Biblical Greek Dictionary
The noun θρονος (thronos) means seat or throne (hence the word throne). It stems from a barely ever used verb θραω (thrao), to set, from which also stems a more common verb θραομαι (thraomai), to be seated, and its derived noun θρανος (thranos), which refers to a kind of bench or rather a support structure upon which floors and such rested — comparable to the word δοκος (dokos), which was found so conspicuous in one's brother's eye.
Our core verb does not simply mean to sit as opposed to stand — that would be covered by the verb ημαι (hemai) — but rather in the sense of to vest. It stems from the Proto-Indo-European root dher-, meaning to hold firmly or to support, which also gave us the familiar Latin adjective firmus (firm) and the Sanskrit dharma, meaning statute or law. It may even have reminded a Greek audience of the noun θαρσος (tharsos), meaning courage, and its adjective θρασυς (thrasus), meaning bold.
Our noun θρονος (thronos) describes a position upon which a governmental authority is centered, which indeed became embodied by the furniture upon which an authority sat. Our word may describe a throne in the regal sense, a chair in the chairman sense, a bench in the judicial sense, and even the seat of a teacher or orator.
For a slightly more elaborate review of the act of sitting, or settling down upon a throne, see our article on the verb καθιζω (kathizo). Our noun is used 61 times in the New Testament; see full concordance.