He felt under-prepared for the presentation because he didn't have enough time.

under-prepared 是由前缀 under-（表示"不足、不够"）和形容词 prepared（准备好的）组成的复合形容词，字面意思是"准备不足的"。under- 这个前缀常用来表示某种程度低于标准或预期。