Thankful for fat mixed with gruel (8)
I believe the answer is:
grateful
'thankful' is the definition.
(similar in meaning)
'fat mixed with gruel' is the wordplay.
'mixed with' is an anagram indicator.
'fat' mixed up with 'gruel' can make 'GRATEFUL'.
'for' acts as a link.
(Other definitions for grateful that I've seen before include "Showing appreciation for kindness" , "Beholden" , "Showing gratitude" , "Felt a rug (anag)" , "Showing thankfulness" .)