Pole, 40, found in analytical exploration initially (4)
I believe the answer is:
axle
'pole' is the definition.
(thesaurus)
'40 found in analytical exploration initially' is the wordplay.
'40' becomes 'xl' (roman numeral).
'found in' means one lot of letters goes inside another.
'initially' indicates taking the first letters.
The initial letters of 'analytical exploration' is 'ae'.
'xl' going inside 'ae' is 'AXLE'.
(Other definitions for axle that I've seen before include "Wheel spindle" , "Shaft with wheels attached" , "It's pivotal" , "Bar on which wheel revolves" , "Shaft on which a wheel rotates" .)