simple past tense and past participle of peak
"The sales figures peaked last month before dropping significantly in February."
somewhat ill or prone to illness
"my poor ailing grandmother"
"feeling a bit indisposed today"
"you look a little peaked"
"feeling poorly"
"a sickly child"
"is unwell and can't come to work"
Having a peak or peaks.
"After weeks of battling the flu, he looked so peaked that his mother insisted on bringing him soup from home."
Sickly-looking, peaky.