Having head of security inside gallery makes sense (5)
I believe the answer is:
taste
'sense' is the definition.
(taste is one of the five senses)
'having head of security inside' is the wordplay.
'having' becomes 'tate' (I can't explain this - if you can you should believe this answer much more).
'head of' says to take the initial letters.
'inside' indicates putting letters inside.
The first letter of 'security' is 's'.
'tate' going around 's' is 'TASTE'.
'gallery makes' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for taste that I've seen before include "A test (anag)" , "one of the 4 [SENSE] s" , "Sense showing refinement" , "Savour in state" , "Sample the flavour" .)