Observed as well most of the cutting edge (8)
I believe the answer is:
sawtooth
'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'.
'saw'+'too'+'th'='SAWTOOTH'
(Other definitions for sawtooth that I've seen before include "(Of waveform) showing linear rise and fall" , "Show a tot (anag.)" , "A jagged edge" , "With jagged outline" , "serrated" .)