Definition of Lewis base in US English:

Lewis base

noun

Chemistry
  • A compound or ionic species which can donate an electron pair to an acceptor compound.

    • ‘In both cases, the ammonia molecule is acting as a Lewis base, donating the pair of electrons required to form the coordinate covalent bond.’
    • ‘In simple additions, the carbonyl compounds can behave as both Lewis acids and Lewis bases depending on what reagents are present.’

Origin

1960s: named after G. N. Lewis (see Lewis acid).