Definition of downmost in English:

downmost

adjective & adverb

British
  • The furthest down; at or towards the bottom.

    ‘If the cuticle was downmost, the water dispersed immediately across the section.’
    ‘Lay the machine on its side with the pump downmost and remove sump and look in pump for obstruction.’

Pronunciation

downmost

/ˈdaʊnməʊst/