Daft students, tense inside (4)
I believe the answer is:
nuts
'daft' is the definition.
(synonyms)
'students tense inside' is the wordplay.
'students' becomes 'NUS' (National Union of Students).
'tense' becomes 't' (abbreviation used in many dictionaries).
'inside' indicates putting letters inside.
'nus' placed around 't' is 'NUTS'.
(Other definitions for nuts that I've seen before include "Mast - mad" , "deprived of one's wits" , "Eccentric; coal lumps" , "Hard-shelled fruits or seeds" , "Crazy (sl.)" .)