A weak excuse is an inadequate or unconvincing explanation for something. The term can be broken down into three crossword solutions: LAME (4 letters), COPOUT (6 letters), and IFORGOT (7 letters). LAME is an adjective meaning of poor quality, unsatisfactory, or inferior. COPOUT is a noun meaning an act of avoiding a responsibility or duty. IFORGOT is a verb meaning to fail to remember or recall something. All three words are used to describe a weak excuse.