monotonous

1. Sounded or spoken in an unvarying tone.
2. Tediously repetitious or lacking in variety. See synonyms at boring.

[From Greek monotonos : mono-, mono- + tonos, tone; see tone.]

adjective

Arousing no interest or curiosity: boring, drear, dreary, dry, dull, humdrum, irksome, stuffy, tedious, tiresome, uninteresting, weariful, wearisome, weary. See excite/bore/interest.

Definition: all the same, remaining the same
Antonyms: changing, ever-changing, exciting, interesting, lively, variable, varied, versatile

The adjective has 2 meanings:

Meaning #1: sounded or spoken in a tone unvarying in pitch
  Synonyms: monotone, monotonic

Meaning #2: tediously repetitious or lacking in variety; all work and no play"
  Synonym: humdrum