Student making love with undies regularly spread (8)
I believe the answer is:
latitude
'spread' is the definition.
(thesaurus)
'student making love with undies regularly' is the wordplay.
'student' becomes 'L' (as in L-plates for learner drivers).
'making love' becomes 'at it' (I've seen this before).
'with' says to put letters next to each other.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'undies' are 'ude'.
'l'+'atit'+'ude'='LATITUDE'
(Other definitions for latitude that I've seen before include "London's is about fifty one point five degrees North" , "a certain line?" , "Imaginary line around the earth parallel to the equator" , "Licence" , "'Leeway, scope (8)'" .)