Small inlet of the sea around Beachy Head (4)
I believe the answer is:
baby
'small' is the definition.
(thesaurus)
'inlet of the sea around beachy head' is the wordplay.
'inlet of the sea' becomes 'bay'.
'around' means one lot of letters goes inside another.
'head' suggests taking the first letters.
The first letter of 'beachy' is 'b'.
'bay' enclosing 'b' is 'BABY'.
(Other definitions for baby that I've seen before include "Love" , "Darling" , "invention" , "about to howl?" , "This 13 [SPICE]" .)