Old bloke picked up sp___ (6)
I believe the answer is:
geyser
'old' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for geyser that I've seen before include "Spring discharging hot water and steam" , "Natural spout of hot water" , "Spring that spouts hot water" , "Gas-fired water heater" , "Spring spurting hot water upwards" .)