Without hesitation, the smallest note (5)
I believe the answer is:
minim
'note' is the definition.
(type of musical note)
'without hesitation the smallest' is the wordplay.
'without' indicates named letters should be taken away.
'hesitation' becomes 'um' (um is said in hesitation).
'the smallest' becomes 'minimum' (I've seen this before).
'minimum' with 'um' taken away is 'MINIM'.
(Other definitions for minim that I've seen before include "Two crotchets in one" , "It's a downward stroke" , "Double crotchet" , "Note equal to two crochets" , "Note with value of half a semibreve" .)