1: A Drug in the Fallout universe.

2: Dissociative drugs or Methamphetamines.

3: Slang: A hormone or neuropeptide supplement based off of natural neurochemistry which temporarily enhances cognitive function, often resulting in a diminished capacity for the user to produce said chemicals naturally.
1: Fallout boy found some illegal mentates in the Vault City administration building.

2: The man in the ally used to be a surgeon before he got burned out on mentates like crystal meth and angel dust.

3: My room mate bought some mentates from the health food store to stay sharp for the big test, now he's suffering a temporary brain crash and can't even solve basic math problems.
by GroundWalker January 8, 2011
Dan will be a poor mentor because he lacks the ability to effectively MentateVerb his mentees on anything other than back of house
by Steve jobs July 2, 2012
A literary reference from Frank Herbert's Dune series describing someone who has been extensively trained to emulate the mental calculating capacity of a computer. Mentats have a tendancy to analyze everything as if it were data for a calculation. This term describes someone who over-analyzes every situation.
"If you could stop being a mentat for just one minute, you'd realize that all I wanted was a kiss..."
by Daniel June 6, 2005