Beast in lair pierced by tick (5)
I believe the answer is:
demon
'beast' is the definition.
(I've seen this before)
'lair pierced by tick' is the wordplay.
'lair' becomes 'den' (synonyms).
'pierced by' indicates putting letters inside (some letters pierce a hole in others).
'tick' becomes 'mo' (both can mean a very short amount of time).
'den' enclosing 'mo' is 'DEMON'.
'in' acts as a link.
(Other definitions for demon that I've seen before include "Wizard" , "Fallen angel" , "ace" , "Skilful person" , "See 3" .)