Meaning of “subtle” - Learner’s Dictionary

subtle

adjective uk us /ˈsʌtl/
NOT OBVIOUS

not obvious or easy to notice:

a subtle hint
NOT STRONG

A subtle flavour, colour, etc is delicate and not strong or bright.

CLEVER

clever in a way that does not attract attention:

a subtle way of solving the problem
subtly adverb

(Definition of “subtle” from the Cambridge Learner’s Dictionary © Cambridge University Press)