lit. tiger's head, snake's tail (idiom); fig. a strong start but weak finish
Definitions (粵典–words.hk)
語句
虎頭大,蛇尾細,比喻做事有始冇終 in like a lion, out like a lamb
宣傳文化嘅活動次次都唔多人響應,最後變到虎頭蛇尾。
宣传文化嘅活动次次都唔多人响应,最后变到虎头蛇尾。
syun1 cyun4 man4 faa3 ge3 wut6 dung6 ci3 ci3 dou1 m4 do1 jan4 hoeng2 jing3, zeoi3 hau6 bin3 dou3 fu2 tau4 se4 mei5. As not many people support cultural activities, they usually ended up with a whimper.
Definitions (Wiktionary)
phrase, idiomatic
to start off strong, but finish weak; to be inconsistent with one's effort