"Do you have a large sum?"
Translation:Tu ai o sumă mare?
I think you are asking why isn't it 'suma marea,' where 'suma marea' in your question means 'the largest sum'?
Sumă = sum Suma = the sum
But mare has a couple meanings, 'large' if you are using it as an adjective or it could also mean 'sea' if you use it as a noun. However when you say marea you are actually saying 'the sea'
Mare is actually feminine as well as masculine in its singular form. It is also one of those adjectives that changes form only in the case of numbers.
Singular masculine and feminine: mare
Plural masculine and feminine: mari