Quake when young chorister crosses minister at first (7)
I believe the answer is:
tremble
'quake' is the definition.
(I know that quake is a more specific form of the action the tremble)
'young chorister crosses minister at first' is the wordplay.
'young chorister' becomes 'treble' (type of singing voice).
'crosses' indicates putting letters inside.
'at first' suggests taking the first letters.
The initial letter of 'minister' is 'm'.
'treble' going around 'm' is 'TREMBLE'.
'when' is the link.
(Other definitions for tremble that I've seen before include "Shudder" , "Shake with fright or cold" , "Shiver, quake" , "get the shakes" , "Show fear" .)