Word Study
ha-ha
CIDE DICTIONARY
ha-ha, n. [See Haw-haw.].
A sunk fence; a fence, wall, or ditch, not visible till one is close upon it. [1913 Webster]
OXFORD DICTIONARY
ha-ha, n. a ditch with a wall on its inner side below ground level, forming a boundary to a park or garden without interrupting the view.
Etymology
F, perh. from the cry of surprise on encountering it
ROGET THESAURUS
ha-ha
Interval
N interval, interspace, separation, break, gap, opening, hole, chasm, hiatus, caesura, interruption, interregnum, interstice, lacuna, cleft, mesh, crevice, chink, rime, creek, cranny, crack, chap, slit, fissure, scissure, rift, flaw, breach, rent, gash, cut, leak, dike, ha-ha, gorge, defile, ravine, canon, crevasse, abyss, abysm, gulf, inlet, frith, strait, gully, pass, furrow, abra, barranca, barranco, clove, gulch, notch, yawning gulf, hiatus maxime, hiatus valde deflendus, parenthesis, void, incompleteness, period, interim (time), with an interval, far between, breachy, rimose, rimulose, at intervals, longo intervallo.For further exploring for "ha-ha" in Webster Dictionary Online