noun (n)

• the exponent required to produce a given number(noun.communication)

  Synonym:
  log
  

  source: wordnet30
• One of a class of auxiliary numbers, devised by John Napier, of Merchiston, Scotland (1550-1617), to abridge arithmetical calculations, by the use of addition and subtraction in place of multiplication and division.(noun)

  source: webster1913