Source : Webster's Revised Unabridged Dictionary (1913)

Ratlines \Rat"lines\, ratlins \rat"lins\, n. pl. [Of uncertain
   origin.] (Naut.)
   The small transverse ropes attached to the shrouds and
   forming the steps of a rope ladder. [Written also {ratlings},
   and {rattlings}.] --Totten.