Final answer:
The noun-forming suffix that forms the plural for words ending in -itis is -ides.
Step-by-step explanation:
The noun-forming suffix that forms the plural for words ending in -itis is -ides. This suffix is responsible for forming the plural of words like arthritides and dermatitides.
For example, the word 'arthritis' becomes 'arthritides' when the suffix is added to indicate multiple instances of the condition. Similarly, the word 'dermatitis' becomes 'dermatitides' when the suffix is applied for pluralization.
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