This question discusses how poison was the first thing that came out of Samudra Manthana. Shiva drank that poison to save everyone and is known as Neelakantha. The poison itself is called हलाहलं (Halahalam) or कालकूटं (KaalaKootam).
I heard that the word हलाहलं is mentioned in different forms in different texts.
Also, this wiki article describes (maybe not correctly) two of the meanings of KaalaKootam as 'black mass' or 'time puzzle'.
Why is the poison given these two names - हलाहलं and कालकूटं ? Is there any hidden symbolism behind it?