Small person - small, hot and terribly prim (6)
I believe the answer is:
shrimp
'small person' is the definition.
(shrimp is a kind of small person)
'small hot and terribly prim' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'hot' becomes 'h' (abbreviation eg on taps).
'and' means one lot of letters go next to another.
'terribly' indicates an anagram.
'prim' is an anagram of 'rimp'.
's'+'h'+'rimp'='SHRIMP'
(Other definitions for shrimp that I've seen before include "little fellow" , "Seafood" , "Diminutive person" , "colour?" , "Small edible crustacean" .)