Definition of overarch in US English:

overarch

verb

[with object]
  • Form an arch over.

    ‘an old dirt road, overarched by forest’
    • ‘The morning light fell upon him, dappled as it was by the trees that overarched us, and revealed the full horror of what he had suffered.’
    • ‘Along the lakefront a curving sweep of barberry and daylilies terminated at gazebos overarched by old apple and willow trees.’

Pronunciation

overarch

/ˌōvərˈärCH//ˌoʊvərˈɑrtʃ/