Boundary

google

ref

early 17th century: variant of dialect bounder, from bound2 + -er1, perhaps on the pattern of limitary .

wiktionary

ref

bound +‎  -ary, Old French, from Latin. 

etymonline

ref

boundary (n.)

"that which indicates the limits of anything," 1620s, from bound (n.1) + -ary. Strictly, a visible mark indicating a dividing line, a bound being the limit or furthest point of extension of any one thing.