Poke about round ultimately fab machine (5)
I believe the answer is:
robot
'machine' is the definition.
(I know that Robot is a type of machine)
'poke about round ultimately fab' is the wordplay.
'poke about' becomes 'root' (I've seen this in another clue).
'round' indicates putting letters inside.
'ultimately' says to take the final letters.
The last letter of 'fab' is 'b'.
'root' placed around 'b' is 'ROBOT'.
(Other definitions for robot that I've seen before include "Automatic worker?" , "Mechanism that moves automatically" , "Lifelike machine" , "Automatic machine" , "Mechanical man" .)