Tabloid (American) sent up GI's sweetheart (5)
I believe the answer is:
sugar
'gi's sweetheart' is the definition.
'sugar' can be an answer for 'sweetheart' (thesaurus). I am not certain of the 'gi's' bit.
'tabloid american sent up' is the wordplay.
'tabloid' becomes 'rag' ('rag' can be a synonym of 'tabloid').
'american' becomes 'us'.
'sent up' says the letters should be written backwards.
'rag'+'us'='ragus'
'ragus' back-to-front is 'SUGAR'.
Can you help me to learn more?
(Other definitions for sugar that I've seen before include "Make more palatable" , "Term of affection" , "Sucrose" , "Damn" , "flattery" .)