Somebody regularly heard weasel (5)
I believe the answer is:
viper
'weasel' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'somebody regularly heard' is the wordplay.
'somebody' becomes 'vip' (I've seen this in another clue).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'heard' are 'er'.
'vip'+'er'='VIPER'
Can you help me to learn more?
(Other definitions for viper that I've seen before include "Venomous snake, person" , "A poisonous snake or treacherous person" , "Adder" , "Malicious person" , "Deadly-venomous snake" .)