Notice one model getting fat (7)
I believe the answer is:
adipose
'fat' is the definition.
('adipose' can be similar in meaning to 'fat')
'notice one model getting' is the wordplay.
'notice' becomes 'ad'.
'one' becomes 'i' (Roman numeral).
'model' becomes 'pose' ('pose' can be a synonym of 'model'**).
'getting' is a charade indicator (letters next to each other).
'ad'+'i'+'pose'='ADIPOSE'
(Other definitions for adipose that I've seen before include "Is a dope fat?" , "Like fatty tissue" , "Relating to fat" , "Composed of animal fat" , "Fat-storing (tissue)" .)