Praise is partly a reflex to love shown (5)
I believe the answer is:
extol
'praise' is the definition.
(extolling is a kind of praising)
'partly a reflex to love shown' is the wordplay.
'partly' indicates a hidden word.
'EXTOL' can be found hidden inside 'reflex to love shown'.
'is' acts as a link.
(Other definitions for extol that I've seen before include "Warmly approve of" , "Sing the praises of" , "Praise highly, laud" , "'Praise, glorify (5)'" , "Lavishly praise" .)