Had unusually sound tips for purchase (8)
I believe the answer is:
adhesion
'purchase' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'had unusually sound tips' is the wordplay.
'unusually' indicates an anagram.
'sound' becomes 'noise' (a noise is a sound).
'tips' says the letters should be written backwards (I've seen 'tipping' mean this).
'noise' reversed gives 'esion'.
'had' with letters rearranged gives 'adh'.
'adh'+'esion'='ADHESION'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for adhesion that I've seen before include "The property of sticking" , "Tackiness" , "Sticking fast" , "strong attachment" , "Process of sticking together" .)