Top definition
1) Derived from the prefix femto, which means ten to the minus fifteen.

2)Stupid; very, very stupid

3)Extremely gullible.

3)Mentally retarded.
The femtobrain spent his rent money on a fortune teller.
by ad-92129 September 05, 2011
Mug icon

The Urban Dictionary Mug

One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.

Buy the mug