to serve as a priest: to hold and carry out the duties of the priestly office before God
TranslatabilityApproximateCertaintySettled
This verb is built directly from the noun for a priest, so it means specifically to function as one: to be set apart to the priesthood and to do a priest's work at the sanctuary. It is not a general word for serving or worshiping. Nearly every time it appears it describes Aaron and his sons being consecrated and ministering in the priestly office, which is why English Bibles so often render it with the whole phrase "minister in the priest's office."
The word carries the sense of official standing as well as activity. To do this is both to occupy the position of priest and to perform its ceremonies, and the two cannot really be separated: a person carries out these duties because he holds the office, and he holds the office in order to carry them out. Where the word is negated, as in the warning to a faithless people and to a disqualified line, it means to be barred from the office altogether.
One poetic passage stretches the picture. Isaiah compares a rejoicing person to a bridegroom who decks himself with a fine headdress the way a priest puts on his ceremonial one, using the verb for the act of donning priestly attire rather than for officiating.
Nuances
1ato officiate as a priest: to hold and perform the work of the priesthood
names the specific work of a priest and the office he holds, not service in generalExo 28:1Exo 40:13
Both
both describe serving in a sacred office before GodExo 29:44
Only minister
the English word "minister" is broad and can mean any servant, attendant, or member of the clergy, and today often suggests a preacher, losing the specifically priestly meaning
“officiate”
Comparison data is not available for this English gloss yet.
How kahan differs from similar Hebrew words
שָׁרַתto minister or attend as a servant of any rank, including Levites and personal attendants, whereas this word means specifically to officiate as a priest
names the specific act of functioning as a priest, the formal office that belongs only to Aaron and his sons, never used for the service of an ordinary attendant.Exo 28:1Exo 29:44
marks the ceremony of setting a man apart into that priestly office, as when Aaron and his sons are anointed and consecrated so they can serve in it.Exo 28:41Exo 40:15
Both
both describe the sanctuary duty carried out by Aaron's sons, named side by side for the finely worked garments made for that duty.Exo 35:19Exo 39:41
is the ordinary word for personal attendance on someone, used just as naturally of a household servant waiting on his master as of any sacred duty.Gen 39:41Ki 1:4
describes an assistant staying close to a leader or prophet, a role open to anyone chosen for it and not limited to Aaron's family.Jos 1:11Ki 19:21
עָבַדto serve, work, or worship in the broadest sense, something any Israelite does, while this word is reserved for holding and performing the priestly office
The word is reserved for the priestly office itself: it names Aaron and his sons being set apart and consecrated to hold and perform the duties of the priesthood, not work of any other kind.Exo 28:1Exo 29:1
It can be negated to describe a man or an entire line being shut out from the priesthood altogether, a standing this word alone marks.2Ch 11:14Hos 4:6
In one poetic verse it is used figuratively of a person decking himself out the way a priest dons his ceremonial headdress, with no actual officiating in view.Isa 61:10
Both
Both can describe work done at the sanctuary by someone specially assigned to it: this word for Aaron's sons being consecrated to hold the priestly office, and the broader word for the priests carrying out the duties tied to that same office once they are consecrated.Num 3:3Num 18:7
It covers ordinary manual and agricultural labor that has nothing to do with the sanctuary, such as tilling the ground or working six days before the Sabbath rest.Gen 2:15Exo 20:9
It names forced labor and slavery, the condition of being worked by a master rather than holding any office.Exo 1:13Lev 25:39
It is the ordinary verb for worshiping or giving allegiance to a god, true or false, open to every person and not tied to any office, including the repeated warning against serving other gods.Exo 20:5Jos 24:15Deu 6:13
kahan in the other biblical languages
ἱερατεύωGreek“to serve as priest”the matching Greek verb for serving as a priest, used of Zechariah taking his turn at the temple
The Hebrew verb is used again and again in the fixed formula for installing a man into the priesthood, naming the act of ordination itself and not merely its later exercise.Exo 28:1Exo 29:44
The Hebrew verb can also be negated, describing a man or an entire priestly line being shut out from serving as priest altogether, a use the single New Testament occurrence never has occasion to show.Ezk 44:13Hos 4:6
The Hebrew verb is also used once in a purely figurative sense, of a person decking himself out the way a priest dons his ceremonial headdress, with no actual officiating in view.Isa 61:10
Both
At bottom both verbs describe a man carrying out the functions of the priestly office: the Hebrew word for Aaron's sons being consecrated to serve at the tabernacle, and the Greek word for Zechariah, centuries later, still serving his turn as a priest in the Jerusalem temple.Num 3:3Luk 1:8
The Greek verb survives only this once in the New Testament, reporting a plain historical fact: the priest Zechariah was taking his turn serving in the Jerusalem temple within the routine rotation of his priestly division, a picture of ongoing service rather than a technical formula for entering the office.Luk 1:8
What scholars say about kahan
The verb is denominative from כֹּהֵן (kohen, "priest") and is attested almost entirely in the piel, where it means to act or officiate as a priest; the lexica (HALOT, BDB) treat it as a single, well-established sense. The overwhelming distribution is the priestly-installation formula לְכַהֵן לִי ("to serve me as priest") across Exodus, Leviticus, and Numbers, extended to the officiating priesthood in the Chronicler and the prophets, and negated for the disqualified or rejected priesthood (2 Chronicles 11:14;Ezekiel 44:13;Hosea 4:6).Isaiah 61:10 is the one figurative use, where יְכַהֵן takes פְּאֵר (a headdress or turban) as its object; BDB and HALOT gloss it there as decking or dressing oneself like a priest, i.e. donning priestly headgear, which is the basis for treating it as a distinct nuance rather than a distinct meaning. TDOT and TWOT discuss the verb under the noun and connect the office to its cultic duties.
Sources
HALOT, s.v. כהןlexicon
BDB, s.v. כהןlexicon
W. Dommershausen, "כֹּהֵן kōhēn," in TDOT 7:60-75reference