Monotonous is a related term of lacklustre.
As adjectives the difference between monotonous and lacklustre
is that monotonous is having an unvarying tone or pitch while lacklustre is (british).
monotonous
English
Adjective
(
en adjective)
having an unvarying tone or pitch
tedious, repetitious or lacking in variety
Related terms
* monotone
* monotony
Synonyms
* monotonic
* samely