Abarim Publications' online Biblical Greek Dictionary
There are two Greek words that are spelled εις, but one is pronounced as (eis) and the other one as (heis).
But note that diacritical marks (that aim to retain pronunciation) didn't exist in Greek until well after the New Testament was written. That means that our two words were wholly identical to the Biblical authors, and differentiated only by context.
The ubiquitous preposition εις (eis) describes a motion into any place or thing, and can often be translated with "in", "into" or "at". It is the opposite of εκ (ek), which describes a motion out of anything, and differs from προς (pros) in that the latter describes the approach while εις (eis) describes the arrival.
In a temporal sense, our word reflects arriving at a certain point in time, and can hence be translated with "up to" or "until". As such, it may also be used to describe the final result of a process (bind them into bundles, Matthew 13:30) or the upper limit of a clause or condition (guilty as hell, Matthew 5:22).
The word εις (heis) is the cardinal number one (Matthew 5:41, Romans 3:12). Its rather curious feminine form is μια (mia), and the neutral is εν (hen), which looks surprisingly similar to the preposition εν (en), meaning in, on or at.
Besides its purely numerical value, our noun may express unity ("one flesh", Mark 10:8) and inclusivity ("each one", Matthew 17:4, Ephesians 5:33, Revelation 21:21). It may mean "even one" (Matthew 5:36), "one and the same" (Romans 3:30), "someone" (Matthew 19:16), "a certain one person" (Mark 14:51). On occasion our word may be used as ordinal number, meaning first (Matthew 28:1).
The neutral form of our word gives rise to the following Biblical derivations:
- Together with δεκα (deka) meaning ten: the cardinal ενδκα (hendeka), meaning eleven (Matthew 28:16, Mark 16:14, Luke 24:9 and 24:33, and Acts 1:26). From this word comes:
- The ordinal ενδεκατος (hendekatos), meaning eleventh (Matthew 20:6, 20:9 and Revelation 21:20 only).
- The noun ενοτης (henotes), meaning oneness or unity (Ephesians 4:3 and 4:13 only).