Like a dunce cap Charlie is given after trick with iodine (5)
I believe the answer is:
conic
'like a dunce cap' is the definition.
(dunce caps are conical)
'charlie is given after trick with iodine' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'is given after' means one lot of letters go next to another.
'trick' becomes 'con' (a con is a fraud or trick).
'with' says to put letters next to each other.
'iodine' becomes 'I' (chemical symbol).
'con'+'i'='coni'
'c' after 'coni' is 'CONIC'.
(Other definitions for conic that I've seen before include "Shaped like an ice cream cornet" , "solid, curved" , "Figure of circle, ellipse, parabola or hyperbola" , "A 99 is thus" , "Pointed" .)