It is entirely possible to know things about God. The general revelation provided by His creation is sufficient to know He is powerful and existent. And, God has revealed Himself and His nature through special revelation (miraculous means, e.g., His Written Word).
So, God can be described. Never in totality, but in His attributes and truths about His nature. You can describe aspects of His nature to others, yet they won't understand who God is or what He is like without a personal relationship with Him.
Even a lifetime spent getting to know Him leaves more to learn. A mere dictionary definition is woefully inadequate and misleading. It's impossible for any finite human to comprehend the true, infinite God.