pleomorphic /plē-ō-mörˈfik/, also pleomorphous /-fəs/

1. Occurring in several different forms, polymorphic
2. Changing form several different times during its life cycle (biology)

• keep one's countenance
• keep one's distance
• keep one's ear to the ground
• keep oneself to oneself
• keep one's end up
• keep one's eye in
• keep one's eye on
• keep one's eyes peeled
• keep one's eyes skinned
• keep one's finger on the pulse
• keep one's fingers crossed
• keep one's hair on
• keep one's hand in
• keep one's head
• keep one's head above water
• keep one's head down
• keep one's mind on
• keep one's mouth shut
• keep one's nose clean
• keep one's options open
• keep one's powder dry
• keep one's shirt on
• keep one's thumb on
• keep one's weather eye open
• keep one's wits about one