This is the 3374th most frequent Japanese word.
染みつい
The word "染みつい" does not exist in standard Japanese. You might mean "染み付く (しみつく)," which means "to be ingrained" or "to become firmly attached."
The word '染みついている' describes the state of being permeated or invested; here, the smell of cigarettes is deeply absorbed into the clothes.
彼の服には煙草の匂いが染みついている。
His clothes are imbued with the smell of cigarettes.
In this sentence, '染みついていた' indicates a concept strongly ingrained or habitually internalized within someone, referring to his deep-seated habit.
その習慣は彼に染みついていたため、変えるのが難しかった。
The habit was ingrained in him, so it was difficult to change.
Here, '染みついてしまった' implies the dirt's persistent presence and absorption over time into the wall's surface.