Old Sam set tests (5)
I believe the answer is:
exams
'tests' is the definition.
('exam' can be a synonym of 'test')
'old sam set' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'set' is an anagram indicator (instruction to set the letters).
'sam' with letters rearranged gives 'ams'.
'ex'+'ams'='EXAMS'
(Other definitions for exams that I've seen before include "School tests" , "summer term commitment?" , "More than one test" , "Set of exercises evaluating knowledge (abbr)" , "GCSE, A-level, etc" .)