Use 'runt' for the smallest, weakest young animal in a group, often struggling for survival. The puppy identified as the runt of the litter required special care.
Pro Tip 2/3
Not Just Size
'Runt' implies a struggle due to being undersized and typically underdeveloped, not just small. The runt often faced more health issues than its siblings.
Pro Tip 3/3
Sentimental Use
In storytelling, the runt can evoke sympathy or be the underdog who overcomes adversity. The runt became the hero of the farm after saving the litter from danger.