Dictionary:

secondhand

  (sĕk'ənd-hănd')

1. Previously used by another; not new.
2. Dealing in previously used merchandise.
3. Obtained, derived, or borrowed from another; not original.

In an indirect manner; indirectly.

Definition: used
Antonyms: new

The adjective has 2 meanings:

Meaning #1: derived from what is primary or original; not firsthand

Meaning #2: previously used or owned by another
  Synonym: used

The adverb secondhand has one meaning:

Meaning #1: by indirect means
  Derived from adjective: secondhand (meaning #1)