Abarim Publications' online Biblical Greek Dictionary
The noun ιματιον (imation) means piece of clothing, and although this word could technically describe any kind of garment it's commonly used to refer to outer garments or overcoats. Another word for overcoat is επενδυτης (ependutes), from the verb δυω (duo), to get into, which could describe one's clothing as much as one's profession, which helped to establish one's mode of dress as indicative of one's mode of occupation.
In the time before advertising, folks dressed according to their jobs, and one could recognize a professional of any kind by his outfit. This means that one's outer garment primarily proclaimed to the world one's abilities and guild. In the New Testament, an outer garment is, per rule, mentioned solely in reference to the wearer's allegiances and associations (Matthew 11:8, 21:7-8). And when the wearer removes his outer garment (when stoning Stephen, for instance; Acts 7:58), he indicates that he acts purely by his own consternation and not from following his party's decrees.
Our noun ιματιον (imation) derives from the more general noun ειμα (eima), which also means outer garment but also covers carpets and rugs, and is related to the noun ιμας (imas), which denotes a leather strap with which to tie something upon something else, for instance a helmet onto a head. Ultimately, these words derive from the Proto-Indo-European root "wes-", to wear or dress, from which also comes the word west — whereas east comes from "aus-", to shine, suggesting that with one's outer garment, one obscured one's own identity in order to be identified by a collective one.
The significance of this continues into the genders, since in the Biblical languages, masculinity describes the tendency to be an individual (which is why God is masculine, also see Matthew 5:9, Galatians 3:26, and so on), whereas femininity describes the tendency to be a collective (which is why humanity as a whole is feminine: Galatians 4:24-26, Ephesians 5:26, Revelation 19:7). This is part of the reason why "women" are not allowed to teach in church (1 Timothy 2:12), and why the 144,000 who followed the Lamb and the Lamb only had "not been defiled with women" (Revelation 14:4). This rather obviously does not refer to proper marital relations but by what Jesus says in Matthew 23:8-12: "Do not call anyone on earth your father; for One is your Father, He who is in heaven. And do not be called leaders; for One is your Leader, that is, Christ."
Beginning believers often think that it's important to be called by the religion one has just joined (Christianity, Islam, Judaism, Buddhism, and so on) or denomination (evangelical, Catholic, whatever), but no, that's not what fidelity to Christ is all about. In Christ there is no Jew, no Greek, no Scythian, no barbarian, and not even male or female, master or slave (Galatians 3:28, Colossians 3:11). There's only one God, one creation and one Word to both describe creation and the Creator (John 1:18, Colossians 1:16-17, Hebrews 1:3). In Christ, all robes are white: with no colors, flags, symbols or other markings of affiliation and segregation (Matthew 17:2, Revelation 7:14).
Our noun ιματιον (imation) occurs 61 times in the New Testament, see full concordance, and from it derives: