General Antonyms:
* Complex: This is a common and direct antonym for "simple."
* Complicated: Similar to complex, but often emphasizing a sense of difficulty or intricacy.
* Intricate: Implies a high level of detail or complexity.
* Elaborate: Suggests a great deal of care and effort has been put into something.
* Sophisticated: Often implies a high level of knowledge, skill, or understanding.
Antonyms Based on Specific Meanings:
* Difficult: If "simple" refers to easiness, then "difficult" is an antonym.
* Unclear: If "simple" refers to clarity, then "unclear" is an antonym.
* Unnatural: If "simple" refers to naturalness, then "unnatural" is an antonym.
* Extravagant: If "simple" refers to frugality, then "extravagant" is an antonym.
* Artificial: If "simple" refers to genuineness, then "artificial" is an antonym.
To choose the most appropriate antonym, consider the specific context in which the word "simple" is used.