Keep check, receiving a word of thanks (6)
I believe the answer is:
retain
'keep' is the definition.
(retaining is a kind of keeping)
'check receiving a word of thanks' is the wordplay.
'check' becomes 'rein' (both can mean to control or limit).
'receiving' is an insertion indicator.
'a word of thanks' becomes 'ta' (informal way of saying thank you).
'rein' placed around 'ta' is 'RETAIN'.
(Other definitions for retain that I've seen before include "Hold onto" , "Keep in Tirane" , "Keep, hold on to something" , "Hold on to or employ counsel" , "Keep possession of" .)