What is the greek words for You reap what you sew?

There isn't a single, perfect Greek equivalent of the English proverb "You reap what you sow" that captures its nuance and is commonly used. The proverb relies on an agricultural metaphor, and while Greek has words for reaping and sowing, a direct translation wouldn't necessarily carry the same weight or be idiomatic.

However, we can construct a phrase that conveys a similar meaning:

Ό,τι σπείρεις, θερίζεις (Ó,ti speíreis, therízeis)

This translates literally to: "Whatever you sow, you reap." It's grammatically correct and understandable, effectively communicating the principle of cause and effect. It's probably the closest you'll get to a direct translation while retaining the meaning. Other similar phrases could be constructed, but this is concise and clear.