big head

Short definition from Wiktionary

Noun

1. 1
   Alternative form of bighead (“person with an inflated opinion of themselves”).
2. 2
   An inflated ego, an exaggerated belief in one's own importance.
3. 3
   The brain, as opposed to the penis, little head; rational thought, as opposed to lust.
4. 4
   The short head of a long tail distribution.
5. 5
   Alternative spelling of bighead.