To dad, some yams are fruit! (6)
I believe the answer is:
papaya
'fruit' is the definition.
(papaya is a kind of fruit)
'to dad some yams are' is the wordplay.
'to dad' becomes 'papa' (synonyms).
'some' indicates taking the first letters.
The first letters of 'yams are' is 'ya'.
'papa'+'ya'='PAPAYA'
(Other definitions for papaya that I've seen before include "Large, green West Indian fruit" , "Oval melon-like tropical fruit" , "Caribbean fruit" , "Tropical fruit with pink flesh and black seeds" , "Fruit with orange flesh" .)