Beautiful female bird crossing sides of lake (5)
I believe the answer is:
helen
'beautiful female' is the definition.
The definition suggests a singular noun which matches the answer.
'bird crossing sides of lake' is the wordplay.
'bird' becomes 'hen' (hen is a kind of bird).
'crossing' is an insertion indicator (to cross can mean to go over or around).
'sides of' means to remove the middle letters (only the letters on the sides remain).
'lake' with its centre taken out is 'le'.
'hen' placed around 'le' is 'HELEN'.
Can you help me to learn more?
(Other definitions for helen that I've seen before include "Was this the face that launch'd a thousand ships?" , "Famous beauty of Troy" , "legendary Greek figure" , "Legendary beauty of Troy" , "Woman who launched a thousand ships?" .)