solely

1. Alone; singly: solely responsible.
2. Entirely; exclusively: did it solely for love.

adverb

1. Without the presence or aid of another: alone, single-handedly, singly, solitarily, solo. Idioms: all by one's lonesome, by oneself. See include/exclude.
2. To the exclusion of anyone or anything else: alone, but, entirely, exclusively, only. See include/exclude.

Definition: only, alone
Antonyms: shared, together

The adverb has one meaning:

Meaning #1: without any others being included or involved
  Synonyms: entirely, exclusively, alone, only
  Derived from adjective: sole (meaning #1)