
merklich
noticeable
Clearly perceptible, noticeable, or visible; in such a way that one can notice it.
Nachdem die Heizung angestellt wurde, wurde es im Raum merklich wärmer.
After the heating was turned on, the room became noticeably warmer.
noticeable
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noticeable
Clearly perceptible, noticeable, or visible; in such a way that one can notice it.
Nachdem die Heizung angestellt wurde, wurde es im Raum merklich wärmer.
After the heating was turned on, the room became noticeably warmer.
'Merklich' (noticeable) comes directly from the verb 'merken' (to notice, to perceive). The ending '-lich' means '-able', so something is 'merklich' when it can be noticed.
Hast du gemerkt, dass es kälter geworden ist?
Did you notice that it has gotten colder?
'Merklich' (noticeable/noticeably) can stand before a noun as an adjective or describe a verb or another adjective as an adverb. As an adverb, its form remains unchanged.
Es gab eine merkliche Verbesserung seiner Noten.
There was a noticeable improvement in his grades.
'Merklich' (noticeable/noticeably) is often used to describe a change or a state. Typical combinations are 'ein merklicher Unterschied' (a noticeable difference), 'eine merkliche Besserung' (a noticeable improvement), or 'merklich kälter/leiser/besser werden' (to become noticeably colder/quieter/better).
Der Unterschied zwischen den beiden Versionen ist nur gering, aber merklich.
The difference between the two versions is only small, but noticeable.
clear / clearly
Deutlich and merklich can describe a perceptible change. Deutlich usually emphasizes its clear or considerable extent. Merklich mainly says that the change has become perceptible or visible, even if it does not have to be particularly large.

Schon nach zehn Minuten war das Zimmer merklich wärmer.
After just ten minutes, the room was noticeably warmer.
Nach einer Stunde war das Zimmer deutlich wärmer.
After an hour, the room was significantly warmer.