Rigid Tom needs a boost (9)
I believe the answer is:
catatonic
'rigid' is the definition.
Although both the answer and definition are adjectives, I cannot see how one could define the other.
'tom needs a boost' is the wordplay.
'tom' becomes 'cat' (a tom is a male cat).
'needs' says to put letters next to each other.
'boost' becomes 'tonic' (tonic can mean a stimulant or booster).
'cat'+'a'+'tonic'='CATATONIC'
Can you help me to learn more?
(Other definitions for catatonic that I've seen before include "In a state of immobility and stupor" , "Rigid and in a stupor through illness" , "Not very lively" , "Stupefied and immobile" , "Behaving abnormally" .)