Saw the Grand Master post each hour (10)
I believe the answer is:
apophthegm
'saw' is the definition.
(I've seen this before)
'the grand master post each hour' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'master' becomes 'M' (common abbreviation eg MA, Master of Art).
'post' says to put letters next to each other (post- can mean after).
'each' becomes 'apop' (eg 'one pound a pop' can mean 'one pound each').
'hour' becomes 'h' (abbreviation).
'the'+'g'+'m'='thegm'
'apop'+'h'='apoph'
'thegm' after 'apoph' is 'APOPHTHEGM'.
(Another definition for apophthegm that I've seen is " Saw".)