We had a profitable discussion that helped clarify our goals.

profitable 是由名词 profit（利润、收益）加上形容词后缀 -able 构成的形容词。profit 指"利润、好处"，-able 表示"能够...的"，所以 profitable 字面意思是"能够带来利润/好处的"，引申为"有益的、有利可图的"。