# Semantically, how does 'before' differ from 'till'?

till {prep. [here] conj., and adv.}

Etymology: [..] Probably originally a noun * til = Old English till fixed point, station [...]
hence the const. with genitive: prop. ‘with the limit or goal of (the place or time named)’. [...]
To the same root belong Old English til adjective ‘to the purpose, serviceable, good’ [...]

II. Of time.
[5] b. After a negative, denoting the continuance of the negative condition up to the time indicated (and implying its cessation then); thus nearly equivalent to before. Cf. B. 1b.

OED's use of the adverb nearly above, implies difference(s) between till and before. So what are these semantic drifts?

Etymologically, till means: TO some fixed point or station. So this 'TO' can be interpreted as approximation to the fixed point/station, without knowing whether the fixed point is attained. Which meanings of before, does this interpretation of till neglect?

• It is not "semantically" but logically and mathematically. This question is relevant for any language, not just English. – Blessed Geek Aug 12 '15 at 3:55

I'll be here till 3.

I'm going to leave before 3.

I hope I understood your question.

Sometimes the two words are more or less interchangeable, but they do have subtle differences.

before

preposition

previous to; earlier or sooner than

Source: Dictionary.com

until

conjunction

up to the time that or when; till

Source: Dictionary.com