Toy dog briefly left by lake (4)
I believe the answer is:
doll
'toy' is the definition.
(doll is a kind of toy)
'dog briefly left by lake' is the wordplay.
'briefly' means to remove the last letter.
'left' becomes 'l' (common abbreviation**).
'by' is a charade indicator (letters next to each other).
'lake' becomes 'l'.
'dog' with its last letter taken away is 'do'.
'do'+'l'+'l'='DOLL'
(Other definitions for doll that I've seen before include "Toy replica of a person" , "Puppet" , "Girl's toy" , "Toy baby" , "Figurine" .)