Fountain (6)
'fountain' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for spring that I've seen before include "Bound; source" , "Season of growth" , "Mechanical device" , "warp" , "The vernal season" .)
(Other definitions for soda that I've seen before include "pressurised liquid" , "Sodium carbonate" , "Mixer drink" , ""Splashed" drinks mixer" , "Drink containing carbonated water and sometimes flavouring" .)
(Other definitions for pen that I've seen before include "Writing implement" , "'The ... is mightier than the sword'" , "Cage - bird" , "Shut up" , "See 20" .)