This book is perfect for intermediate language learners who want to expand their vocabulary.

intermediate 由前缀 inter-（表示"在...之间"）和词根 medi（意为"中间"）组成，加上后缀 -ate 构成形容词，字面意思是"处于中间的"。在这里指语言学习者的水平处于"初级和高级之间"，即"中级的"。