Function at first absolutely no good being held in marquee? (7)
I believe the answer is:
tangent
'function' is the definition.
(I know that tangent is a type of trigonometric function)
'first absolutely no good being held in marquee?' is the wordplay.
'first absolutely' becomes 'a' (1st letter of 'absolutely').
'no good' becomes 'ng' (abbreviation for no and good).
'being held in' indicates putting letters inside.
'marquee?' becomes 'tent' (marquee is a kind of tent).
'a'+'ng'='ang'
'ang' placed into 'tent' is 'TANGENT'.
'at' acts as a link.
(Other definitions for tangent that I've seen before include "Line grazing another" , "seen to be touching" , "Particular line" , "Straight line that touches but does not intersect a circle" , "A new line of thought" .)