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Webster 1913 Edition

adv.

In an ideal manner; by means of ideals; mentally.

adv.

Intellectually; mentally; in idea.

ideally ‎(comparative more ideally, superlative most ideally)

In an ideal way; perfectly. [from 18th c.]
- 2004, Richard Fortey, The Earth, Folio Society 2011, p. 46:
  The summit of Mauna Kea is considered the ideal place to mount an astronomical observatory, for above the clouds there is only the stars and the skies are ideally transparent.
Given ideal circumstances; preferably. [from 19th c.]

preferably