tooth: one of the teeth in the mouth, whether of a person or of an animal
This word means "tooth" and nothing else. There is no second sense to untangle, no hidden theological freight in the noun itself. What is worth noticing is not the range of the word but where it turns up: of its twelve appearances in the New Testament, nine describe teeth being ground or clenched together.
Seven of those nine are a single fixed phrase, "weeping and grinding of teeth," which Jesus uses for people shut out of God's kingdom. It is a set expression, always the same words, and the teeth in it are not really the subject. They are the sound of a reaction, dropped in where a plainer writer might simply have said "misery."
The remaining appearances are ordinary and easy to picture:
- a tooth counted as an injury under the old rule of "a tooth for a tooth"
- a crowd baring its teeth at Stephen in open hatred as they close in on him
- a boy's teeth grinding together while his body is seized by a fit
- the teeth of the locust creatures in a vision, said to be like a lion's
The Hebrew word standing behind "a tooth for a tooth" (שֵׁן) covers rather more ground than the Greek does: besides the tooth in the mouth it can mean ivory, or a jutting crag of rock shaped like a tooth. The Greek stays with the tooth.