youngest

1. In the early part of growth or life; born not long ago.

   a lamb is a young sheep;  these picture books are for young readers

2. At an early stage of existence or development; having recently come into existence.

   the age of space travel is still young;   a young business

3. (Not) advanced in age; (far towards or) at a specified stage of existence or age.

   How young is your dog?   Her grandmother turned 70 years young last month.

4. Junior (of two related people with the same name).
5. (of a decade of life) Early.
6. Youthful; having the look or qualities of a young person.

   My grandmother is a very active woman and is quite young for her age.

7. Of or belonging to the early part of life.

   The cynical world soon shattered my young dreams.

8. Having little experience; inexperienced; unpracticed; ignorant; weak.

noun

The youngest child in a family, or individual in a group.