Transience of intrinsic nature said to follow Welshman (11)
I believe the answer is:
evanescence
'transience' is the definition.
(evanescence is a kind of transience)
'intrinsic nature said to follow welshman' is the wordplay.
'intrinsic nature' becomes 'essence' (essence can mean something's nature or core).
'said' indicates a 'sounds like' (homophone) clue.
'to follow' means one lot of letters go next to another.
'welshman' becomes 'evan' (common Welsh name).
'essence' is a homophone of 'escence'.
'escence' after 'evan' is 'EVANESCENCE'.
'of' is the link.
(Other definitions for evanescence that I've seen before include "tendency to pass rapidly" , "Transient quality" , "Fading" , "A quick vanishing" .)