Unsuitable function I recalled hosting President (5)
I believe the answer is:
inapt
'unsuitable' is the definition.
(I've seen this before)
'function i recalled hosting president' is the wordplay.
'function' becomes 'tan' (tangent, mathematical function).
'recalled' shows that the letters should be reversed in order (to recall can mean to bring something back).
'hosting' means one lot of letters goes inside another (inserted letters are welcomed in or hosted).
'president' becomes 'p' (common abbreviation eg in VP).
'tan'+'i'='tani'
'tani' backwards is 'inat'.
'inat' enclosing 'p' is 'INAPT'.
(Other definitions for inapt that I've seen before include "Inappropriate" , "not seemly" , "unqualified" , "Cartoon duck" , "It's clumsy" .)