Retainable is a word that often describes something that can be kept or maintained over time. Synonyms for retainable include durable, lasting, sustainable, enduring, and long-lasting. These words all convey the idea of something that can be preserved or maintained for an extended period of time. Other possible synonyms for retainable may include enduring, permanent, unchangeable, and immovable. Each of these words describes something that can be maintained, preserved, or held onto for an extended period of time, and can be useful when trying to describe something that lasts or can be maintained over time.