a sandal: a sole strapped under the foot, the ordinary footwear people walked in
TranslatabilityApproximateCertaintySettled
The word literally names what is bound underneath: a leather sole held to the foot by straps. That was the everyday footwear of the ancient world, cheap and universal, and the Greek term covers footwear in general rather than one particular style, which is why English Bibles move between "sandals" and "shoes" without either being wrong. Greek has a second word for footwear (σανδάλιον), used the same way in the Gospels, and the two are interchangeable.
Sandals carried the dust of the road, so handling another person's was the dirtiest job in a household and fell to the lowest slave. John the Baptist reaches for exactly that picture when he says he is not fit to carry the sandals of the one coming after him, or even to stoop down and untie their straps. The point is not modesty about his own preaching but distance in rank.
The word also turns up wherever footwear marks a person's standing or a place's holiness:
the father puts sandals on the returning son's feet, restoring him as a son rather than a hired hand
Moses is told to take his off, because the ground where he is standing is holy
the disciples are sent out without a spare pair, so that they depend on the towns that receive them
This is the word in John the Baptist's saying about the one coming after him: he is not worthy to untie the strap of the man's footwear, or even to carry it. Handling another person's footwear was the job of the lowest slave in a household, so the word carries the whole weight of that self-abasement, and all four Gospels plus Paul's sermon in Acts use this word for it.Mat 3:11Mrk 1:7Luk 3:16Jhn 1:27Act 13:25
It is the word for footwear that must come off in God's presence. When Stephen retells the burning bush, the Lord tells Moses to loosen the footwear from his feet because the ground he is standing on is holy.Act 7:33
It can stand for restored standing in a household. The father orders footwear for the returning son's feet along with the best robe and the ring, since going barefoot marked a slave or a beggar rather than a son.Luk 15:22
It is the ordinary word for footwear as one of a traveler's supplies, listed alongside the purse and the bag that the disciples were sent out without.Luk 10:4Luk 22:35
Both
Both name the same everyday footwear, so completely that the Gospels use one word or the other for the same instruction. Mark reports Jesus sending the Twelve out wearing this footwear with one word, while Matthew reports the same charge, telling them not to take it, with the other. English simply says "sandals" for both.Mrk 6:9Mat 10:10
Both name footwear that is fastened to the foot with a strap rather than an enclosed shoe. The angel tells Peter to bind his on, and John speaks of the strap that would have to be untied.Act 12:8Jhn 1:27
Both times it appears, someone is being told to put footwear ON and get moving. Jesus lets the Twelve travel shod, and the angel tells Peter to strap his footwear on and follow him out of the prison. It never shows up in a command to take footwear off or to leave it behind.Mrk 6:9Act 12:8
In the New Testament it stays a plain object and nothing more. Neither verse turns the footwear into a picture of rank, worth, or holiness the way the other word repeatedly does; it is simply what a traveler wears on his feet.Mrk 6:9Act 12:8
hupodēma in the other biblical languages
נַעַלHebrew“sandal”the Hebrew word for a sandal, which this word translates in the command to Moses at the burning bush, and which also carries a legal use in transfers of property and family duty.
The object of a servant's lowest task: to untie or carry another's sandals, the image John the Baptist uses to measure how far below the coming one he stands.Mat 3:11Mrk 1:7Jhn 1:27Act 13:25
Part of the travel kit a sent-out worker is told to carry or leave behind, in Jesus' instructions to those he commissions.Mat 10:10Luk 10:4Luk 22:35
Both
Both name the ordinary sandal worn on the foot, taken off as a sign that the ground one stands on is holy.Exo 3:5Act 7:33
A legal token in the levirate and redemption ceremonies: drawing off the sandal renounces or seals a transaction, and the shamed man's line is branded "the house of him whose sandal was pulled off."Deu 25:9Rut 4:7Rut 4:8
A gesture of ownership or contempt flung over conquered territory: "over Edom I toss my sandal."Psa 60:8Psa 108:9
The trivial price for which the poor are sold, a byword for injustice: the needy handed over "for a pair of sandals."Amo 2:6Amo 8:6
What scholars say about hupodēma
BDAG and LSJ give ὑπόδημα a single sense, "sandal," the noun being formed from ὑποδέω, "to bind under," and denoting the sole fastened beneath the foot; LSJ documents the term's wider classical and Hellenistic use for footwear generally, which is why the word and σανδάλιον are not consistently differentiated. In the sending traditions ὑπόδημα stands at Matt 10:10;Luke 10:4; 22:35 where Mark 6:9 has σανδάλιον, and commentators (Davies and Allison; Marshall; Nolland) treat the two as naming the same object, the difference in the Markan instruction lying in whether the sandals are already worn rather than in the item named. The Baptist's saying about carrying or loosing the sandal strap (Matt 3:11;Mark 1:7;Luke 3:16;John 1:27;Acts 13:25) is standardly explained against the rabbinic ruling (b. Ketub. 96a) that excludes untying the master's sandal from the services a Hebrew slave owes, so that the Baptist assigns himself a station beneath a slave's; see Davies and Allison on Matt 3:11 and Keener on John 1:27.Acts 7:33 reproduces the Septuagint of Exod 3:5, where ὑπόδημα renders נַעַל, and Luke 15:22 reflects the widespread association of bare feet with slavery, poverty, or mourning.
Sources
BDAG, s.v. ὑπόδημαlexicon
LSJ, s.v. ὑπόδημαlexicon
EDNT, s.v. ὑπόδημαtheological-dictionary
W. D. Davies and Dale C. Allison, A Critical and Exegetical Commentary on the Gospel according to Saint Matthew, ICC, vol. 1 (Edinburgh: T&T Clark, 1988), on Matthew 3:11 and 10:10commentary
I. Howard Marshall, The Gospel of Luke, NIGTC (Grand Rapids: Eerdmans, 1978), on Luke 3:16 and 10:4commentary
John Nolland, Luke 1-9:20, WBC 35A (Dallas: Word, 1989), on Luke 3:16commentary
Craig S. Keener, The Gospel of John: A Commentary, vol. 1 (Peabody, MA: Hendrickson, 2003), on John 1:27commentary