Irretentive is often used to describe someone or something that lacks the ability to remember or retain information. Here are a few synonyms for this word that capture the same essence. Firstly, we have "forgetful", which refers to the tendency to easily forget things. Another synonym is "inattentive", which signifies a lack of focus or attention, leading to poor retention. "Unretentive" is another option, emphasizing the inability to retain knowledge or memories. Additionally, "absent-minded" characterizes individuals who often forget or become distracted easily. Lastly, "unmindful" describes someone who is not mindful or attentive to details, resulting in a lack of retention. All these synonyms represent the same concept of being irretentive.