Master worried about helping relative (13)
I believe the answer is:
proportionate
'relative' is the definition.
(similar in meaning)
'master worried about helping' is the wordplay.
'master' becomes 'pro' ().
'worried' becomes 'ate' (something worrying may eat someone up).
'about' says to put letters next to each other.
'helping' becomes 'portion' (synonyms).
'ate' put after 'portion' is 'portionate'.
'pro'+'portionate'='PROPORTIONATE'
(Other definitions for proportionate that I've seen before include "each component should be this!" , "Corresponding in size or amount to something else" , "in scale" .)