Dairy product initially of great help in tent (7)
I believe the answer is:
yoghurt
'dairy product' is the definition.
(I know that yoghurt is a type of dairy product)
'initially of great help in tent' is the wordplay.
'initially' suggests taking the first letters.
'in' means one lot of letters goes inside another.
'tent' becomes 'yurt' (I've seen this in other clues).
The initial letters of 'of great help' is 'ogh'.
'ogh' going inside 'yurt' is 'YOGHURT'.
(Other definitions for yoghurt that I've seen before include "Semi-liquid food" , "cultural production" , "Dairy produce" , "Fermented milk product" , "Tory? Ugh! (anag)" .)