It sounds similar to (or identical to, probably, if you have a particular accent) "maudlin"--meaning excessively sentimental; weak and silly--and has "mad" in it, as in "insane" If you like a Madeline sort of name, just pick Madeline, so at least it won't end up tacky and dated.
I love this name! Its so old world celtic style. Im getting ready to name our baby this. Ill spell it differently but gotta keep the family name going! Madlyn is a beautiful name and its not all used up in the states. Who cares how you spell it if its nice sounding name the go for it! Madlyn mae:) how come madilee or matlee isnt here?