Clement worried by tendency to blow top (9)
I believe the answer is:
temperate
'clement' is the definition.
(similar in meaning)
'worried by tendency to blow top' is the wordplay.
'worried' becomes 'ate' (something worrying may eat someone up).
'by' says to put letters next to each other.
'tendency to blow top' becomes 'temper' (a tendency to blow one's top or get angry).
'ate' put after 'temper' is 'TEMPERATE'.
(Other definitions for temperate that I've seen before include "comfortably warm?" , "pleasant" , "It is reasonable" , "Continent" , "Showing self-restraint" .)