Final answer:
The word 'weirdo' corresponds best with a) 'eccentric' since both describe someone with an unusual or odd character that is typically harmless. 'Madman', 'lunatic', and 'psychotic' reference more severe mental conditions and are not equivalent.
Step-by-step explanation:
The word "weirdo" is used to refer to someone who is unusually strange or eccentric. Among the given choices, the one that best matches the word "weirdo" is a) eccentric. This is because 'eccentric' describes a person who has an unconventional or odd character, often harmlessly or endearingly.
On the other hand, 'madman', 'lunatic', and 'psychotic' imply a more serious mental condition, which can be offensive when used casually or inaccurately to describe someone's peculiar behavior that is not related to a mental illness.