We don't have synonyms for spring line yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are springlike, spring tide and firing line.
(n) :
(nautical) A line stretched longways between a docked vessel and a cleat on the pier, or used during berthing to guide the vessel into its slip; a warp
(n) :
(architecture) A line above which an arch starts curving inward.
(n) :
(nautical) A line stretched longways between a docked vessel and a cleat on the pier, or used during berthing to guide the vessel into its slip; a warp
(n) :
(architecture) A line above which an arch starts curving inward.