Hot spring (6)
I believe the answer is:
geyser
'hot spring' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for geyser that I've seen before include "Spring that spouts hot water" , "Gas-fired water heater" , "Spring spouting steam and hot water" , "It gushes steam and hot water" , "Spring that discharges steam and hot water" .)