Observed as well most of the cutting edge (8)
I believe the answer is:
Here is my best explanation:
'cutting edge' is the definition.
(edge of a saw)
'observed as well most of the' is the wordplay.
'observed' becomes 'saw' (I've seen this before).
'as well' becomes 'too' (synonyms).
'most of' means to remove the last letter.
'the' with its final letter removed is 'th'.