Drink in short pitcher starts to loosen everyone's principles (5)
I believe the answer is:
julep
'drink' is the definition.
(julep is a kind of drink)
'in short pitcher starts to loosen everyone's principles' is the wordplay.
'in short' means to remove the last letter.
'pitcher' becomes 'jug' (I've seen this before).
'starts to' suggests taking the first letters.
The first letters of 'loosen everyones principles' is 'lep'.
'jug' with its final letter removed is 'ju'.
'ju'+'lep'='JULEP'
(Other definitions for julep that I've seen before include "Cocktail of bourbon, sugar and mint over crushed ice" , "Mint drink in America" , "See 21 Down" , "Sweet drink, often medicated" , "(Minted) drink made with bourbon, sugar and crushed ice" .)