By the time he sought help, he had already become an alcoholic.

alcoholic 是由名词 alcohol（酒精）加上后缀 -ic 构成的形容词，表示"与酒精有关的"或"酒精引起的"。作为名词时指"酗酒者"或"酒精成瘾者"。 后缀 -ic 常用于将名词转化为形容词，表示"与...有关的"或"具有...特性的"。