puer·il·ism 
(pyrə-lĭz′əm, pwĕrə-, pyər-ə-)
(pyrə-lĭz′əm, pwĕrə-, pyər-ə-)n.
Childish behavior in an adult, especially as a symptom of mental illness.
- insensitive
- insensitively
- insensitiveness
- insensitivity
- insentience
- insentient
- inseparability
- inseparable
- inseparableness
- inseparably
- in series
- insert
- inserter
- insertion
- insertional
- in-service
- insessorial
- inset
- inshallah
- inshore
- in short
- in short order
- inshrine
- inshrine
- Inshta Theumba ("Bright Eyes").