Stick a designating initial on present (6)
I believe the answer is:
adhere
'stick' is the definition.
('adhere' can be a synonym of 'stick')
'a designating initial on present' is the wordplay.
'initial' indicates taking the first letters.
'on' says to put letters next to each other.
'present' becomes 'here' ('here' can be similar in meaning to 'present'**).
The first letter of 'designating' is 'd'.
'a'+'d'+'here'='ADHERE'
(Other definitions for adhere that I've seen before include "secure" , "Bond" , "paste" , "Stick or cleave to" , "Hold fast, stand by" .)