monotonic
mo-no-ton-ic
adjective
Lacking variation in pitch or tone; dull and unvarying.
"His monotonic voice made the lecture boring."
adjective
Always increasing, always decreasing, or remaining constant in value.
"The function showed a monotonic increase over time."
Thesaurus
Synonyms: increasing monotonic, decreasing monotonic, monotone, unmodulated, flat, monotonous
Antonyms: nonmonotonic